4.7a Comparison of strength values, material costs, and ease of field ...... From Mohr's circle construction, it is evident that shear strength or cohesion ... because it is this that is to be protected from damage by building a pavement ..... is not responsive to cement alone in its natural state (Punmia 2005). ...... Engineer Manual.
PEAT STABILIZATION
Behzad Kalantari University of Hormozgan – Bandar Abbas
LAP LAMBERT academic publishing GmbH & Co. KG. Germany (2012) ISBN 978-3-8484-1720-9
ii
Dedicated to Civil Engineers (Involving constructions on peat)
iii
iv
PREFACE
This book presents a laboratory research on stabilizing tropical fibrous peat, and is organized in five chapters. Chapter one introduces the need for this study which includes, the aim, scope, and methodology. Chapter two is literature review on general, as well as specific properties of different types of peat in general and fibrous peat in particular. In this chapter different stabilization methods using ordinary Portland cement with or without additives to stabilize peat conducted by researchers are presented. Chapter three describes the methodology used to fulfil the designated objectives for the research. This chapter includes discussions on field tests, sampling procedures, and continues with the required laboratory tests on some of the most significant physical, chemical, and mechanical properties of plain fibrous peat, as well as stabilized or treated fibrous peat. Also at the end of this chapter a testing program for the field and laboratory works is presented. In chapter four results from various type of tests used for shallow and deep stabilization carried out during the course of the research are presented and analysed in graphical forms. Chapter five summarizes the research methodology and also presents the obtained results that are followed by specific conclusions. Also a list of recommendations for possible future studies is listed at the end of this chapter. Additional information is provided in four appendices as well.
v
vi
ACKNOWLEDGEMENT
The completion of this work would not have been possible without the help and support of many sincere individuals and also great financial support from Research University grants (RUGS) provided by University Putra Malaysia (UPM). Some of the individuals who worked for UPM and whose help will always be remembered are:
Prof. Bujang Bin Kim Huat (Civil Engineering Dept.) Mr.Yoong
-
(GDS com. technician)
Mr. Mohd Razalli B. Rahman (Soil mechanic lab.) Mr. Aminaddin Hamdan (Water lab.) Mr. Mohd Halim B. Osman (Concrete lab.) Mr. Mohd Pairus B. Ismail (Concrete lab.) Dr. Arun Prasad (Post doctoral scholar, from Banaras Hindu University, India) Eng. K.A. Ang (GDS com. Malaysia) Mr. Chen Chin Lai (YTL cement, Malaysia) Mrs. Azizah
-
(Bioscience lab.)
Mrs. Norzuwana Wahab (Dep. Secretary) Mrs. Norhidayah Mad halid (Former Dept. Secretary) Ms. Norasiah Rosli (Soil lab assistant) Mr. Imran Abdul rahim (BSc student) Mr. Yeong Jit Ming (BSc student) Mr. Mohd Kamarul Bin Sarkani (BSc student) Mr. Shahrul Naam Mohd Ali (BSc student) Mr. Ahmad Redha Sharom (BSc student) vii
Also, I would like to extend my special gratitude to LAP LAMBERT Academic Publishing GmbH & Co. KG for their effort to publish this work as well.
viii
TABLE OF CONTENTS Page DEDICATION PREFACE ACKNOWLEDGEMENT LIST OF TABLES LIST OF FIGURES LIST OF SYMBOLS AND ABBRIVIATIONS
iii v vii xiii xv xxvii
CHAPTER 1.0
INTRODUCTION 1.1 1.2 1.3 1.4 1.5
2.0
Introduction Problem statement Objectives Significance of the study Scope of the study
1 2 3 4 4
LITERATURE REVIEW 2.1 2.2 2.3 2.4 2.5 2.6
Introduction Classification of organic soil and peat Fibrous peat Distribution of peat 2.4.1 Distribution of peat in world 2.4.2 Distribution of tropical peat in Malaysia Description of peat Engineering properties of peat 2.6.1 Water content, Atterberg limits, linear shrinkage, and grain size distributions 2.6.2 Density and specific gravity 2.6.3 Fiber content 2.6.4 Loss on ignition and organic content 2.6.5 Permeability 2.6.6 Compaction 2.6.7 Unconfined compressive strength (UCS) 2.6.8 California bearing ratio (CBR) 2.6.9 Triaxial 2.6.10 Consolidation 2.6.11 Field strength evaluation tests 2.6.12 pH 2.6.13 Scanning electron microscopy (SEM) 2.6.14 Energy dispersing x-ray analysis (EDXA) 2.6.15 Field sample collections ix
7 7 9 10 10 11 11 12 14 14 14 14 15 15 16 17 20 24 27 29 30 31 32
2.7
Soft ground improvement 2.7.1 Binding agents 2.7.2 Additives 2.7.3 Cementitious mechanism in soil stabilization 2.8 Traditional curing types for cement treated peat 2.9 Peat stabilization 2.10 Conclusions 3.0
34 35 37 46 48 48 56
METHODOLOGY 3.1 3.2 3.3 3.4
3.5
3.6 3.7 3.8
3.9 3.10
3.11 3.12 3.13 3.14
Introduction Sampling location Soil sampling Index property determination tests 3.4.1 Field identification tests 3.4.2 Moisture content 3.4.3 Consistency limits 3.4.4 Organic content 3.4.5 Grain size distribution 3.4.6 Specific gravity 3.4.7 Fibre content 3.4.8 Linear shrinkage 3.4.9 pH 3.4.10 Moisture-unit weight relation (compaction) Mechanical properties determination tests 3.5.1 Permeability 3.5.2 Unconfined compressive strength (UCS) 3.5.3 California bearing ratio (CBR) 3.5.4 Consolidation undrained (CU) triaxial 3.5.5 Rowe cell consolidation Static load bearing capacity test Field vane shear test Shallow (mass) stabilization of fibrous peat 3.8.1 Mixtures preparation for strength evaluation tests 3.8.2 Types of curing techniques 3.8.3 Linear volume shrinkage index (LVSI) Test to determine time for saturation by soaking in water Deep stabilization of fibrous peat 3.10.1 Preparation of precast stabilized peat columns, and samples for CU tests 3.10.2 Preparation of precast stabilized peat columns, and samples for Rowe cell consolidation tests Preparation of precast stabilized peat columns for load bearing capacity tests Triaxial and Rowe cell tests on precast stabilized column made of hemic and sapric peat SEM and EDX tests for untreated, and OPC treated peat Testing programs x
59 59 61 63 64 64 65 65 66 67 68 68 69 70 71 72 72 74 75 76 76 82 84 84 87 92 94 95 96 99 101 105 106 107
4.0
RESULTS AND DISCUSSION 4.1 4.2
4.3 4.4 4.5
Introduction Results organization 4.2.1 Evaluating the engineering properties of untreated fibrous peat as control measures 4.2.2 Air cured OPC treated fibrous peat strength gain versus conventional curing techniques 4.2.3 Strength gain of OPC treated fibrous peat when used with various additives 4.2.3.a1 Effect of propylene fibres in strengthening OPC treated fibrous peat 4.2.3.a2 Optimum polypropylene fibers (PPF) dosage rate determination 4.2.3.a3 Least soaking period to saturate stabilized samples 4.2.3.a4 UCS and CBR values of OPC and polypropylene fibres (PPF) treated fibrous peat using peat’s natural moisture content 4.2.3.a5 Use of OPC, PPF and optimum moisture content (OMC) values to strengthen fibrous peat 4.2.3.b1 Effect of silica fume (SFU) or micro silica in strengthening OPC treated fibrous peat 4.2.3.b2 Optimum silica fume (SFU) dosage rate determination 4.2.3.b3 UCS and CBR values of OPC, and silica fume (SFU) treated fibrous peat using peat’s natural moisture content 4.2.3.b4 Use of OPC, silica fume (SFU) and optimum moisture content (OMC) values to strengthen fibrous peat 4.2.3c Effect of steel and polypropylene fibres (StF, and PPF) to strengthen OPC treated fibrous peat 4.2.3d Effect of ground granulated blast furnace slag (BFS) in strengthening OPC treated fibrous peat 4.2.3e Effect of fly ash (FA) in strengthening OPC treated fibrous peat 4.2.4 Reinforcing fibrous peat with precast stabilized peat columns to increase load bearing capacity, and to reduce settlement of fibrous peat Liquid limits for stabilized hemic and sapric peat Comparison of various techniques to stabilize fibrous peat Reproducibility of samples
xi
109 109 110 114 117 117 118 120 121 129 136 137 139 141 144 150 155 167 186 187 195
5.0
CONCLUSIONS AND RECOMMENDATIONS 5.1 5.2
Conclusions Recommendations for future researches
REFERENCES APPENDICES A B C D
197 204 207 217 225 233 237
xii
LIST OF TABLES Table
Page
2.1
Classification of organic soil based on range of organic content
8
2.2
Classification of peat on the basis of degree of decomposition
8
2.3
USDA classification of peat
9
2.4
Percentage of area covered by peat in different countries in rank order 11
2.5
Standard correction factors for strength of cylinders with different ratios of height to diameter
2.6
17
General rating of pavement foundations based on their CBR values and their uses
2.7
18
Angle of internal friction (φ) values for various inorganic soils based on triaxial tests
2.8
22
Shear strength parameters of various types of organic soil and peat in Malaysia based on laboratory shear box test results
2.9
Friction angles for various types of fibrous peat based on triaxial compression tests
2.10
23
23
Main components and chemical compositions of ordinary Portland cement
36
2.11
Portland cement types and their uses
37
2.12
Influencing parameters to classify fly ash
40
2.13
Physical Properties of silica fume
41
2.14
Polypropylene fibres specifications
44
2.15
Hooked steel fibres specifications
45
2.16
Strength enhancing reactions for Portland cements and chemical xiii
additives
46
4.1
Properties of untreated peat
113
4.2
Consolidated undrained shear strength parameter values for undisturbed fibrous peat, and different types of precast stabilized fibrous peat columns reinforcing undisturbed fibrous peat samples
167
4.3
Main parameters used for FEM analysis
178
4.4
Index properties of hemic and sapric peats
181
4.5
Consolidated undrained shear strength parameter values for different types of precast stabilized hemic or sapric columns reinforcing undisturbed fibrous peat samples
182
4.6
Definitions of various notations used in Tables 4.7 a, and 4.7b
188
4.7a
Comparison of strength values, material costs, and ease of field applicability levels for various methods proposed by past researchers to stabilize fibrous peat
4.7b
189
Comparison of strength values, material costs, and ease of field applicability levels used in current study to stabilize fibrous peat
4.8
190
Comparison of strength values, material costs, and ease of field applicability levels using various types of columns proposed by various researchers to stabilize fibrous peat
4.9
192
Results for obtained CBR values using optimum moisture contents 194
xiv
LIST OF FIGURES Figure
Page
2.1
Typical CBR results
19
2.2
Mohr – Coulomb failure envelope for obtaining the limiting soil shear strength parameters
2.3
21
Procedure of determining Cc, Cr, and p c from void ratio versus log pressure curve
2.4
26
SEM images of fibrous peat samples at initial state, a) horizontal section, b) vertical section
2.5
31
Schematic of thin-walled (Shelby) tube and photo of tube with end caps
33
2.6
UPM peat sampler
34
2.7
Polypropylene fibers; a) SEM image, b) Photograph showing the discrete short PP-fibre
2.8
43
Sketch of mechanical behavior at the interface between fibre surface and soil matrix
2.9
44
Schematic diagram of concrete blocks performances under load a) plain concrete and b) Steel fibres reinforced concrete
45
2.10
Hooked end steel fibres a) dimensions, b) photograph
45
3.1
Flow chart of the research
60
3.2
Distribution of peat land in Malaysia, and sampling
3.3
location for the research Sampling collection procedures for undisturbed samples (a, b, and c), and for disturbed bulk samples (d) for xv
62
disturbed bulk samples
63
3.4
A test pit to measure the depth of ground water table
64
3.5
Liquid limit (cone penetration) test
65
3.6
Organic content samples in the furnace
66
3.7
prepared peat sample for sieve analysis test
67
3.8
Saturated peat samples in desiccator for specific gravity test
3.9
68
Linear shrinkage test samples a) Before drying, and b) After being dried
69
3.10
Digital calibrated pH probes
69
3.11
Moisture content reduction process of field peat (a) Gradual moisture content reduction or half drying of peat procedure in the oven, and (b) Reduced moisture content samples to be used for compaction tests
3.12
71
Unconfined compressive strength samples, a) Undisturbed sample, b) Reconstructed treated peat (peat mixed with cement) sample after mixing, c) Unsoaked samples, d) Soaked samples
3.13
73
Treated CBR peat samples at their a) air curing, and b) air cured and then soaked conditions, before being tested for their CBR strength values
3.14
Computerized consolidated undrained triaxial test in Progress
3.15
75
76
Details of Rowe cell consolidation test: a) Schematic diagram of Rowe Consolidation cell xvi
b) Rowe Cell consolidation test set-up c) Computerized Rowe cell consolidation in progress, d)A sample after complete consolidation process inside disassembled Rowe cell 3.16
78
A saturated sample inside the prepared steel mould during saturation period, and, prior to be placed in Rowe cell for consolidation
78
3.17
Schematic diagram of the test tank
80
3.18
Schematic loading diagram procedure during load bearing capacity tests
3.19
81
Geonor H-60, hand-held field shear vane tester (units in mm)
3.20
83
Hand –held field vane tester is being used to measure the undrained shear strength of peat at various depths
83
3.21
UCS samples in air curing condition
89
3.22
UCS samples in moist curing condition
89
3.23
Moist curing plus 10 kPa surcharge load procedure; a) plastic tube moulds, b) moulded samples are submerged in water, mortar cylinders, steel weight, and plate are also shown, c) concrete cylinders are placed over the submerged samples, d) the steel weight is placed on top of the concrete cylinders on a plate to exert a total of 10 kPa load on each sample
3.24
91
90 days, air cured shrunken stabilized CBR samples after easily removal from their standard sized moulds, and prior to be securely placed in flexible CBR mould for CBR test xvii
93
3.25
A shrunken stabilized sample is wrapped and clamped securely in the prepared flexible mould prior to being tested for CBR
3.26
93
Moulding precast columns; a) Non-reusable moulds (plastic tubes) made for columns, b) Compacting a layer of mixture in the mold, c) Dried columns out of their moulds
3.27
97
Installation of precast columns; a) Thin-walled metal tube cutters used to make hole at the centre of undisturbed peat samples, b) Precast stabilized peat column to be inserted in the center of triaxial undisturbed peat sample, c) Triaxial undisturbed sample with the precast stabilized peat column placed at its centre
99
3.28
Precast peat columns and non-reusable plastic moulds
100
3.29
Columns installation procedure; a) Undisturbed peat sample, b) Thin walled metal tube cutters inserted in the undisturbed peat sample, c) Sample with hole prepared for the column, d) Stabilized peat column inserted in the undisturbed peat sample
3.30
101
Load bearing capacity tests procedures; a) Compacting the stabilized sample in the mould, b) A moulded cement treated column, c) Moulded columns inside the oven, d) A precast stabilized column prior to be installed inside the test tank, e) Installed column in the test tank, and prior to be tested, f) Load bearing capacity test in progress
3.31
103
FEM loading model for a) plain peat, b) Plain peat reinforced xviii
with 200 mm diameter column, c) Plain peat reinforced with 300 mm diameter column
105
3.32
Oxford, INCA machine instrument used for SEM and EDX tests
106
4.1
Ground subsurface profile
111
4.2
FVS tests values versus depth
112
4.3
General particle size distribution of peat used in the research
4.4
113
UCS values vs. OPC treated samples for 28 days under different curing conditions
4.5
114
UCS values vs. OPC treated samples for 90 days under different curing conditions
4.6
115
UCS values vs. OPC treated samples for 180 days under different curing conditions
4.7
115
UCS increase ratios (%) vs. different amount of different amount of ordinary Portland cement, with various dosage rate of polypropylene fibres
4.8
119
Percent increase and actual CBR values vs. different amount of ordinary Portland cement, with various dosage rate of polypropylene fibres
120
4.9
Percentage weight increase vs. time for soaked CBR samples
121
4.10
Unconfined compressive strength (UCS) values for fibrous peat and 5% OPC with and without polypropylene fibres (PPF) vs. curing time
4.11
122
Unconfined compressive strength (UCS) values for fibrous peat and 15% OPC with and without polypropylene fibres xix
(PPF) vs. curing time 4.12
122
Unconfined compressive strength (UCS) values for fibrous peat and 20% OPC with and without polypropylene fibers (PPF) vs. curing time
4.13
123
Unconfined compressive strength (UCS) values for fibrous peat and 30% OPC with and without polypropylene fibres (PPF) vs. curing time
4.14
123
Unconfined compressive strength (UCS) values for fibrous peat and 50% OPC with and without polypropylene fibres (PPF) vs. curing time
124
4.15
UCS values of various types of plain fibrous peat vs. curing period 124
4.16
Moisture contents reductions versus curing periods for various types of treated fibrous peat samples
4.17
127
CBR (%) values for the undisturbed peat and different percentage of OPC and polypropylene fibres for the stabilized peat cured for 90 days
4.18
129
Dry density-moisture curves: (a) Untreated fibrous peat and fibrous peat stabilized with cement (b) Treated fibrous peat with PP fibres only and fibrous peat stabilized with cement and PP fibres
4.19
131
Unsoaked CBR values for stabilized fibrous peat samples treated with0.15% Polypropylene fibres and different amount of ordinary Portland cement at different air curing period
4.20
Soaked CBR values air cured at 90 days for stabilized fibrous peat with various amount of ordinary Portland cement, and xx
133
0.15% polypropylene fibres 4.21
134
Scanning electron micrograph of; a) original plain fibrous peat, b) stabilized fibrous peat with 5% OPC, and 0.15% PPF, c) stabilized fibrous peat with 15% OPC, and 0.15% PPF, d) stabilized fibrous peat with 30% OPC, and 0.15% PPF
4.22
135
Degree of intactness in cement treated CBR samples with (L), and without inclusion of polypropylene fibres (R) reinforcements
4.23
136
Percentage increase in UCS/actual UCS values versus different percentages of cement and silica fume
4.24
Percentage increase in CBR/actual CBR values versus different percentages of cement and silica fume
4.25
140
Dry density-moisture curves, for treated fibrous peat with different amount of ordinary Portland cement, and silica fume
4.28
139
CBR values for different percentages of ordinary Portland cement and silica fume for unsoaked and soaked samples
4.27
138
UCS values for different percentages of ordinary Portland cement and silica fume for unsoaked and soaked samples
4.26
138
142
CBR values for treated fibrous peat with 5, and 10% silica fume, and various amount of ordinary Portland cement cured for 1, 28, and 90 days (unsoaked)
4.29
143
Soaked CBR values air cured at 90 days for stabilized fibrous peat with various amount of ordinary Portland cement, and silica fume
143 xxi
4.30
Unsoaked and soaked unconfined compressive strength values for fibrous plain peat and fibrous peat (FPt) with 5% cement ordinary Portland cement (OPC) with and without 0.15% of polypropylene fibres (PPF), as well as 2% steel fibres (StF) cured for three months
4.31
146
Unsoaked and soaked and soaked unconfined compressive strength values for fibrous peat plus 15% ordinary Portland cement (OPC) with and without 0.15% of polypropylene fibres (PPF), as well as 2% steel fibres (StF) cured for three months
4.32
146
CBR values of fibrous plain peat samples, as well different types of stabilized peat samples containing 0.15% polypropylene fibres (PPF) and 2 or 4% steel fibres (StF) with 5% OPC, cured for 1, 28 (unsoaked), and 90 days (unsoaked, and soaked)
4.33
148
CBR values of different types of stabilized fibrous peat samples containing 15% cement with 0.15% polypropylene fibres (PPF)and 2 or 4% steel fibres (StF), cured for 1, 28 (unsoaked), and 90 days (unsoaked, and soaked)
4.34
149
CBR values of different types of stabilized fibrous peat samples containing 30% cement with 0.15% polypropylene fibres (PPF), and 2% steel fibres(StF), cured for 1, 28 (unsoaked), and 90 days (unsoaked, and soaked)
4.35
Degree of intactness in OPC treated UCS samples, with and without inclusion of polypropylene fibres
4.36
149
150
Unconfined compressive strength for various types xxii
of stabilized fibrous samples with and without blast furnace slag 4.37
151
Dry density-moisture curves, for treated fibrous peat with different amount of ordinary Portland cement, and blast furnace slag
4.38
152
CBR values of different types of stabilized fibrous peat samples treated with ordinary Portland cement, and blast furnace slag cured for 1, 28 (unsoaked), and 90 days (unsoaked, and soaked)
4.39
153
Unconfined compressive strength for various types of stabilized fibrous samples with and without fly ash
4.40
156
Dry density-moisture curves, for treated fibrous peat with different amount of ordinary Portland cement, and fly ash
4.41
157
CBR values of different types of stabilized fibrous peat samples treated with ordinary Portland cement, and fly ash cured for 1, 28 (unsoaked), and 90 days (unsoaked, and soaked)
4.42
158
Linear shrinkage for various types of stabilized fibrous peat with ordinary Portland cement, silica fume, and polypropylene fibres
4.43
162
Linear volume shrinkage indices for various types of stabilized fibrous peat with ordinary Portland cement, and silica fume
4.44
163
Linear volume shrinkage indices for various types of stabilized fibrous peat with ordinary Portland cement, and different additives 164
4.45
Liquid limits for various types of samples
165
4.46
pH values for various types of samples
166 xxiii
4.47
Variation of deviator stress with axial strain in CU tests, a) Undisturbed, and stabilized samples with OPC with or without polypropylene fibres columns, b) Samples stabilized with OPC and additives (silica fume, blast furnace slag and fly ash) columns
4.48
168
Stress/ strain ratios for untreated sample and reinforced samples with different types of precast columns
169
4.49 Modified compression index (Ccε), values for undisturbed fibrous peat, and samples stabilized with various types of columns 4.50
171
Compression ratio (Crε), values for undisturbed fibrous peat, and samples stabilized with various types of columns
171
4.51
Load – deformation curves
175
4.52
Loading and unloading for plain fibrous peat and fibrous peat reinforced with OPC treated 300 mm precast column
177
4.53 Comparison of deformation values found from actual load bearing tests and FEM analysis for three types of tested samples 4.54
179
Effective principal stress diagrams, (a) Plain fibrous peat, (b) Fibrous peat reinforced with 15% OPC treated 200 mm diameter column and (c) Fibrous peat reinforced with 15% OPC treated 300 mm diameter column
180
4.55
Particle size distribution for hemic peat
181
4.56
SEM for a) sapric, and b) hemic peats
182
4.57
Variation of deviator stress with axial strain in CU tests for various types of samples
183 xxiv
4.58
Stress – Strain ratios for various types of samples
4.59
Modified compression index, and recompression ratio
184
(Ccε and Crε) values for various types of samples
185
4.60
Liquid limits for different types of stabilized samples
186
4.61
Reproducibility samples for UCS tests
196
xxv
xxvi
LIST OF SYMBOLS AND ABBREVIATIONS
av
Coefficient of compressibility
c
Cohesion
c′
Effective cohesion
c′ u
Effective cohesion (from CU tests)
Cc
Compression index
Cr
Recompression index
Ccε
Modified compression index (compression ratio, CR)
Crε
Recompression ratio (or RR)
Cs
Swelling index
Cα
Secondary compression index
Cv
Coefficient of vertical consolidation
Do
Initial diameter
E
Modulus of elasticity
e
Void ratio
eo
Initial void ratio
H
Height
Ho
Initial height
Have
Average height
Hdr
Drainage height
k
Permeability coefficient
kvo
Initial coefficient of permeability
Lo
Initial length
LL
Liquid limit xxvii
LS
Linear shrinkage
mv
Coefficient of volume compressibility
N
Ignition loss
PI
Plastic index
PL
Plastic limit
qu
Unconfined compressive strength
Po or σn
Overburden pressure
Pc
Preconsolidation pressure
su
Total undrained shear strength
s′u
Effective undrained shear strength
R
Radius
T50
Consolidation time factor
t50
Time for 50% consolidation
u
Pore pressure
w/c
Water-cement ratio
γ
Unit weight
γsat
Saturated unit weight
γunsat
Unsaturated unit weight
γdry
Dry unit weight
γdmax
Maximum dry unit weight
γ′
Effective unit weight
γn
Natural unit weight
γw
Unit weight of water
w
Water content xxviii
wn
Natural water content
wopt
Optimum moisture content
σ
Total stress
σ′
Effective stress
φ
Internal friction angle
φ′u
Effective undrained friction angle
ε
Strain
ψ
Dilatancy angle
R2
Coefficient of determination
C
Cement
D
Diameter
L
Length
W (%)
percent moisture content
LS
Linear shrinkage
Co. In
Compression index
GWT
Ground water table
LVSI
Linear volume shrinkage index
OC
Organic content
OPC
Ordinary Portland cement
PC
Portland cement
Fib.pt
Fibrous peat
FPt
Fibrous peat
HPt
Hemic peat
SaPt
Sapric peat
StF
Steel fibres xxix
SFU
Silica fume
PPF
Polypropylene fibres
BFS
Blast furnace slag
GGBS
Ground granulated blast slag
GGS
Ground granulated slag
FA
Flay ash
AR
Area ratio
ICR
Inside clearance ratio
CBR
California bearing ratio
UCS
Unconfined compressive strength
FVST
Field vane shear test
CU
Consolidated undrained (triaxial)
CD
Consolidated drained (triaxial)
UU
Unconsolidated undrained (triaxial)
kN
Kilo Newton
kPa
Kilo Pascal
kg
Kilogram
g or gr
Gram
Mg
Mega gram (1000 kg)
OMC
Optimum moisture content
MDD
Maximum dry density (maximum dry unit weight)
LBC
Load bearing capacity
LIR
Load increment ratio
St
Sensitivity
SEM
Scanning electron microscopy xxx
EDX
Energy dispersing x-ray
FEM
Finite element method
FRC
Fibre reinforced concrete
RCT
Rowe cell consolidation test
PLT
Plate load test
PCC
Precast stabilized peat columns
xxxi
xxxii
CHAPTER 1
INTRODUCTION
1.1
Introduction
Hawkes and Webb (1962), define soil as “any loose surface material overlying solid rock”, thus the concept of soil includes not only the detritus of weathered rocks and accumulation of inorganic sediments, rather includes organic peats and plant roots as well. According to the Oxford Dictionary, peat is a soft black or brown substance formed from decaying plants (Oxford University Press 1995). Peat deposits are the partly decomposed and fragmented remain of plants that have accumulated under water and fossilized, and consist of 50 – 90% organic substances: they are excessively moistened.
These features determine their polyfunctional nature. Botanists and geobotanists study the specific features of bog vegetation on peat soils and the climatic characteristics of the period of the peat accumulation based on the stratigraphy of peat deposits, and they define peat as bogs. Geologists explore peat reserves for industrial purposes and consider peat bogs as peat fields (economic deposits). Hydrologists study the hydrological regime of bogs and determine them as water bodies. Foresters study bogs from the position of improving the quality class of forest stands and call them forest bogs. Soil scientists study peat as agricultural highly fertile soils (Soper and Osbon 1922; Radforth 1969; Babel 1975; Stanek and Worley 1983; Moore 1989; Van der Heidjden et al. 199; and Inisheva 2006).
To civil engineers peat is an example of extreme type of soft soil, and is usually called a problematic type of soil, and they characterize peat deposits with the following behaviours (Huat 2004). a) High natural water content
1
b) High compressibility c) Low shear strength d) Potential for further decomposition as a result of changing environmental condition
Also peat in general show: high liquid limit, low density, relatively low plasticity, and different particle size distribution compared with inorganic soils. It is therefore understandable any kind of civil engineering construction is usually avoided when facing peat lands. However, peat is found in many countries around the globe. In US, peat is found in 42 states, with a total acreage of 30 million hectares (each hectare is 10,000 m2). Canada and Russia are the two countries with the largest area of peat, 170 and 150 million hectares respectively. Tropical peat cover a total of 30 million hectares of the world land, where two third is located in Southeast Asia. Malaysia has some 3 million hectares (about 8%) of her land covered with tropical peat (Duraisamy et al. 2007).
Due to population increase, and demand for social improvements, and therefore land scarce, there is a strong feeling among geotechnical engineers to find ways to strengthen this type of weak soil while keeping the project cost as low as possible.
1.2
Problem statement
Peatlands (muskeg) or organic train have presented difficult subsurface conditions for construction of roads, dikes, housing developments, storage facilities, industrial parks, and so on, including high initial cost and/or continued maintenance operation (Colley 1950; Thomson 1957; MacFarlin 1969; Hanrahanm and Rogers 1981). 2
Peat grounds have two very fundamental interrelated problems as far as their engineering response to load bearing behaviours are concerned. First they have low bearing capacity, and second they undergo large settlements upon loading for almost any types of civil engineering construction projects. Organic soils in general and peat in particular are considered unstable.
Large areas of land all over the world are covered by problematic soils such as peat, in one hand, and increasing population and land scarce in another hand suggest that geotechnical engineers should try to find ways to upgrade the behaviour of problematic soils upon imposed loads as much as possible. Present information indicates that throughout the world organic soils covers 436.2 million hectares of which 35.8 million hectares (8.2 percent) are in tropical and subtropics. The total area of tropical peat land in the world amounts to about 30 million hectares, two third of which is in Southeast Asia (Alwi 2007). Based on reports of many researchers such as Foott and Ladd 1981, Fox and Edil 1996, Mesri and Ajlouni 2007, Huat 2005, and Duraisamy et al. 2007 among three types of peat namely, fibric or fibrous, hemic, and sapric; fibrous peat deposits display extreme compressibility to an increase in effective vertical pressure.
Therefore, it is possible to consider fibrous peat, the most unstable among three types of problematic peat upon imposed loads. Various techniques used to stabilize fibrous peat so far, are limited to few stabilization techniques. In general, knowledge regarding fibrous peat stabilization lacks of new techniques, and materials, that can improve the performances of fibrous peat due to imposed loads, and are relatively easy to apply in real situation and in the field conditions as well.
1.3
Objectives
The broad objective of this research is to stabilize fibrous peat by adopting the following methods: 3
1 – To evaluate the engineering properties of fibrous peat 2 – To evaluate the advantages of air curing technique over the conventional curing methods, namely; moist curing and moist curing with surcharge load 3 – To evaluate the strength of air cured OPC treated fibrous peat with the inclusion of the following additives: a) Polypropylene fibres b) Silica fume c) Steel fibres d) Blast furnace slag e) Fly ash 4 – To evaluate strength and compressibility behaviours of plain fibrous peat reinforced with precast stabilized peat columns
1.4
Significance of the study
Significance of this research includes:
a) To upgrade fibrous peat from a problematic soil to a less problematic soil b) To contribute extra knowledge to the stabilization of peat
1.5
Scope of the study
The primary purpose of this study is to strengthen tropical fibrous peat ground and the scope of the study includes: 1- To collect disturbed and undisturbed samples from Kampung Jawa, Selangor, located in the western part of Malaysia 4
2- To use ordinary Portland cement ( type I )as the binding material 3- To use chemically active (silica fume, blast furnace slag, and fly ash ), as well as chemically non active (polypropylene and steel fibres) additives in conjunction with cement and peat 4- To perform CBR and UCS as strength evaluation tests 5- To cure the stabilized samples up to 180 days 6- To perform consolidation undrained triaxial, and Rowe cell consolidation tests, and to evaluate the shear strengths, and compressibility behaviours of reinforced undisturbed peat respectively 7- To perform laboratory modelled plate load tests on reinforced and remoulded (reconstructed) peat
5
CHAPTER 2
LITERATURE REVIEW
2.1
Organic soils and peat
Any material that contains carbon is called “organic”. However, engineers and geologists use more narrow definition when applying the term to soils. An organic soil is one that contains a significant amount of organic material recently derived from plant remains. This implies it needs to be fresh and still in the process of decomposition, and thus retain a distinctive texture, colour and odour. The term peat refers to highly organic soils that is accumulated and derived primarily from partially decomposed and disintegrated plant remains which have been fossilized under conditions of incomplete aeration and high water content. Physico - chemical and biochemical processes cause these organic materials to remain in a state of preservation over a long period of time. It normally has a dark brown to black colour, a spongy consistency, and an organic odour. Plant fibres are sometimes visible but in the advanced stages of decomposition, they may not be evident. Organic soils with more than 75% organic content are considered peat. Peat is usually found as an extremely loose, wet, unconsolidated surface deposit which forms as an integral part of a wetland system, therefore; access to the peat deposit is usually very difficult as the water table exists at, near or above the ground surface (Huat 2004).
2.2
Classification of organic soil and peat
According to Huat (2004), organic soils are more difficult to subdivide. Based on unified soil classification system (USCS), organic soils are recognized as separate soil entity and have a major division called highly organic soils (pt), which refers to peat, muck and highly organic type of soils. 7
Jarret (1995) gives a classification for organic soils, which can be integrated with the USCS to bridge the gap between peat, and purely inorganic soils that is shown in Table 2.1. Table 2.1: Classification of organic soil based on their organic content (Jarret 1995)
Another useful tool to classify organic soils or peat is based on their fibres content as well as their humification (decomposition) of the fibres. von Post (1920) proposed a classification system (Table D1, Appendix D), which is based on a number of critical factors such as degree of humification, botanical composition, water content, content of fine and coarse fibres and woody remnants. There are 10 degrees of humification (H1 to H10) in the von Post classification system that are determined based on the appearance of soil water that is extruded when the soil is squeezed in the hand. A more summarized version of von Post classification guideline that is also in part proposed by Malaysian soil classification systems for engineering purposes is shown on Table 2.2.
Table 2.2: Classification of peat on the basis of degree of decomposition (Karlson and Hansbo 1981; Jarret 1995)
8
The U.S department of agriculture (USDA) classifies peat in three-point scale with respect to fibre content that is determined by ASTM D 1997 test and is the result of decomposition process of peat materials. This type of classification is shown in Table 2.3. Table 2.3: USDA classification of peat (Huat 2004)
Also American association of state and highway transportation officials (AASHTO), as well as federal aviation administration (FAA) classify peat as A-8.
2.3
Fibrous peat
Among three types of peat, namely: fibric, hemic and sapric, fibric or fibrous peat generally has very high natural water content due to its natural water-holding capacity. Soil fabric, characterized by organic coarse particles, holds a considerable amount of water because the course particles are generally very loose, and the organic particle itself is hollow and largely full of water. Previous researches have indicated that high water content of fibrous peat results in high buoyancy and high pore volume leading to low bulk density and low bearing capacity (Huat 2004; Islam 2009).
Compression of fibrous peat continues at a gradually decreasing rate under constant effective stress, and this is termed as the secondary compression. The secondary compression of peat is thought to be due to further decomposition of fibre which is conveniently assumed to occur at a slower rate after the end of primary consolidation. Based on the definition of Edil (2003), fibrous peat is peat with high organic and fibre content with low degree of humification. Also Landva, and La Rochelle (1983), describe fibrous peat
9
particles consisting of fragments of long stems, thin leaves, rootlets, cell walls, and fibres, and often are quite large.
2.4
Distributions of peat
Peat deposits accumulate wherever the conditions are suitable, that is, in areas with excess rainfall, and the ground is poorly drained, irrespective of latitude. Nonetheless, peat deposits tend to be most common in those regions with a comparatively cool, wet climate. Usually water logged poorly drained conditions not only favour the growth of a particular type of vegetation but also help preserve the plant remains (Huat 2004). Climate changes affect plant growth in peatlands. A period in which increased rainfall occurs enhances peat growth and development. In contrast, along drier period where water levels fall, peat at the surface shrinks and wastes whilst the peat below is compacted. 2.4.1
Distribution of peat in world
Peat is found in many countries around the globe. Canada and Russia are the two countries with a large area of peat, 170 and 150 million hectares respectively (Duraisamy 2008; Alwi 2007; and Huat 2004). Table 2.4 shows distribution of peat deposits throughout the world.
10
Table 2.4: Percentage of area covered by peat in different countries in rank order (Harden and Wolski 1996; Mesri et al. 2007)
2.4.2
Distribution of tropical peat in Malaysia
According to Table 2.4, Malaysia ranks 10th among the countries for its peatland area cover. Tropical peat occurs in both high and low land; however, the highland organic soils are not as extensive as in the low land area. In Peninsular Malaysia, they are found in the coastal areas of the east as well as the west coast of the peninsular. These types of peat deposits are generally termed as basin (produced in high lands), and valley (produced in low land) peats. Basin peat is usually found on inward edge of mangrove swamps along a coast. The depth of peat is generally shallower near the coast and increases inward locally may exceed more than 20 m. A balance of rainfall and evaporation is critical to their sustainability. Basin peat forms domes as much as 15 m whilst valley peat is flat or interlayer with river deposit (Mutallib et al. 1991).
2.5
Description of peat
Hobbs (1986) and Edil (1977) suggested the following characteristics to be included for a full description of peat. a) Colour, which indicates the state of peat 11
b) Degree of humification. c) Water content d) Fibre content e) Liquid limit and plastic limit f) Principal plant component, namely coarse fibre, fine fibre, amorphous
granular material
and woody material
2.6
Engineering properties of peat
In order to identify major components of any types of soils and determining soil engineering properties, it is essential to conduct various types of tests. These tests may be divided to physical and mechanical tests. Physical tests begin with visual inspection of the soil, as far as soil’s appearance, colour, odour, and plasticity are concerned. These methods, however, represent only the first step in adequate description of soil material. They must be supplemented by other procedures leading to quantitative results that may be related to the physical properties with which the engineer is directly concerned (Peck et al. 1974). After visual inspection of soil, tests that usually follow are index property tests and mechanical property tests. Index property test of peat include: a) Water content b) Atterberg Limits c) Linear Shrinkage d) Grain size distribution e) Density and Specific Gravity f) Fibre content g) Loss on ignition and organic content
12
And, mechanical tests which usually are followed by index property tests include: a) Permeability b) Compaction c) Unconfined compressive strength (UCS) d) California bearing ratio (CBR) e) Triaxial f) Consolidation g) Field strength evaluation tests i) Vane shear test ii) Simulated field static plate load test Based on the results reported by researchers such as Hashim and Islam (2008b), as well as Fong and Mohamed (2007) degree of acidity is a significant parameter to chemically strengthen organic soils in general, and peat in particular, and as this degree is reduced and hence alkalinity is increased, more suitable environment is produced for the strengthening process to take place. Also, the microstructures along with chemical elements of stabilized soils (inorganic or organic) before and after stabilization are studied for the changes that were taken during the stabilization process. Also, tests that are usually used to fulfil the mentioned parameters in this section include: a) pH b) Scanning electron microscopy c) Energy dispersing x-ray analysis
13
2.6.1
Water content, Atterberg limits, linear shrinkage, and grain size distributions
The tests mentioned in this section are among those preliminary tests that are commonly conducted on any soil upon its arrival in soil mechanic laboratories. These tests are considered essential to identify the type of soil, and are usually done using their respective ASTM, or British standards. 2.6.2
Density and Specific gravity
Specific gravity of soil solids can be tested in the laboratory using the specific gravity bottle method (ASTM D 854). Density or unit weight is a useful soil parameter to analyse soil behaviour. Based on Huat (2004, and 2005a), and Kaniraj (1988), specific gravity of various types of peat may range from as low as 1.07 and up to around1.8. 2.6.3
Fibre content
One of the parameter that is most often used to classify peat is their fibre content. Fibre content is determined typically from dry weight of fibres retained on sieve # 100 (> 0.15 mm opening size) as percentage of oven dried mass (ASTM D 1997). 2.6.4
Loss on ignition and organic content
Organic matter of any type of soil can be determined using ASTM D 2974. Organic content influences many of the physical, chemical and biological properties of soils. Some of the properties influenced by organic matter include soil structure, soil compressibility and shear strength. In addition, it also affects the water holding capacity, nutrient contributions, biological activity, and water and air infiltration rates. Generally, organics are carbon-based compounds created by natural decomposition and it is the
14
most important parameter for peat, because it set them apart from the other type of soil (silt and clay). Skempton and Petley (1970), find quation 2.1 between ignition loss and organic content: OC (%) = [1 – 1.04 (1 – N)] ×100
Eq. (2.1)
Where OC = organic content (%) N = ignition loss (%)
2.6.5
Permeability
Permeability or hydraulic conductivity of soils is represented by coefficient of permeability (k) and is defined as the rate of discharge of water at a temperature of 20 ºC under conditions of laminar flow through a unit cross-sectional area of a soil medium under a unit hydraulic gradient. Based on ASTM D 2434, there are two types of laboratory tests for determining k: constant head, and falling head tests. The constant-head test is used principally for coarse-grained soils (clean sands and gravels) with k values greater than about 10 ×10-4 cm per sec, while the falling-head test is generally used for less pervious soils (fine sands to fat clays) with k values less than 10 x 10-4 cm per sec (US. Dep. of the Army 1990). Peat deposits exist at very high void ratios because peat particles are porous, and surficial peat deposits have experienced very small effective overburden pressures. Because of their large pore sizes and large void ratios, only clean sands display permeabilities higher than those of fibrous peat (Mesri, and Ajlouni 2007).
2.6.6
Compaction
Compaction of soil is the process by which the solid particles are packed more closely together, usually by mechanical means, thereby increasing the dry unit weight of the soil. Compaction tests are conducted in laboratory to obtain the moisture-density relation for a given compactive effort on a 15
particular type of soil. ASTM D 698 and AASHTO T180 D describe the procedures for obtaining the moisture density relation for finer soils such as silty or clayey soils using compaction or modified compaction tests. Based on modified compaction tests using 15.2 cm diameter, with compactive hammer of 44.5 N, five soil layers, and 56 blows on each layer, the maximum dried density (MDD), as well as optimum moisture content (OMC) of the soil can be detected from the moisture- dry density curve.
2.6.7
Unconfined compressive strength (UCS)
Compressive strength test resolves the suitability of soil for treatment and compares suitability of different mixtures. In the unconfined compression test a cylindrical specimen of cohesive soil is subjected to a steadily increasing axial compression until failure occurs. The axial force is the only force applied to the specimen. The test is normally carried out on 38 mm diameter specimens, but can also be performed on specimens up to 100 mm diameter (B.S 1990). It is suitable only for saturated, non-fissured cohesive soils. Unconfined compressive strength test is described by ASTM 2166, and is widely used for a quick, economical mean of obtaining the approximate shear strength of a cohesive soil. From Mohr’s circle construction, it is evident that shear strength or cohesion (c) of a soil can be approximately computed as; c = qu/2
Eq. (2.2)
Where qu is always as the symbol for unconfined compressive strength of the soil. This computation is based on the fact that the minor principal stress (σ3) is zero (atmospheric), and the angle of internal friction (φ) of the soil is assumed zero (Bowles 1978). In very plastic soils in which the axial stress does not readily reach a maximum value, an axial strain of 20 % is used as the criterion of failure. British standard (B.S 1377) suggests that nominal specimen diameters normally range from 38 mm to 16
100 mm. The specimen length should be as close to twice the diameter as the nature of the soil and the end preparation will permit. The length may vary from 8 % under-size to 12 % over-size without significantly affecting the results. On the other hand, ASTM standard offers Table 2.5 as correction factors for strength of cylinders with different ratios of height to diameter. Table 2.5: Standard correction factors for strength of cylinders with different ratios of height to diameter (ASTM C 42-90)
This test is been used by many researchers such as: Hebib, and Farrell (2003), Axelsson et al. (2002), Chen, and Fong (2008), Hashim, and Islam (2008a, 2008b), Huat et al. (2005a), and Alwi (2007) for strength evaluation of plain peat as well as cement treated peat and soft soils.
2.6.8
California bearing ratio (CBR)
The ratio (expressed as a percentage) of the force required to cause a circular piston of 1935 mm
2
cross-sectional area to penetrate the soil from the surface at a constant rate of 1 mm/min, to the force required for similar penetration into a standard sample of crushed rock. The ratio is determined at penetrations of 2.5 mm, 5.0 mm and the higher value is used (BS 1990). One of the most important parameters to determine in any pavement design is the strength of the underlying subgrade because it is this that is to be protected from damage by building a pavement and it is that has the greatest influence on the structural design (Sese et al. 2005). In pavement design, CBR value is needed and the design thickness of the pavement materials is based on the CBR value of the subgrade (Austoroads 2001). The structural capacity of the subgrade soil can be defined in terms 17
of CBR, and also the design CBR for soil subgrade will be recommended as the lowest value obtained from the laboratory tests (Kentucky 2007). Many paving-design procedures are published in which one enters a chart with the CBR number and reads directly the thickness of subgrade, base course, and/or flexible pavement thickness based on the expected wheel loads (Yoder 1959). Usually, CBR number is used to rate the performance of soils primarily for use as bases and subgrades beneath pavements of roads and airfields. Table 2.6 gives typical ratings of CBR values as well as their possible use as base, subbase, or subgrade (Bowles 1978). Table 2.6: General rating of pavement foundations based on their CBR values and their uses (Bowles 1978)
Typical load-penetration curves are shown in Figure 2.1. The loads required causing penetrations of 2.5 and 5 mm are recorded and expressed as ratios of the loads to cause the same penetrations in a "standard" crushed rock material, the load-penetration curve for which is also included in Figure 2.1. For various reasons the initial part of the penetration curve may be concave, as shown for test 2 shown in Figure 2.1. In such a case the load-penetration curve is projected back to the horizontal axis, as shown in the Figure, to give the intercept A. This intercept is added to the standard penetrations of 2.5 and 5 mm when evaluating the loads equivalent to those penetrations for the materials under test. No such addition is of course made in obtaining the corresponding loads for the standard crushed stone material. The larger of the ratios corresponding to the 2.5, and 5 mm penetrations is normally taken as the CBR value of the material for the test conditions used. The test is usually carried out on materials with a maximum particle size of 20 mm. If the material to be tested contains 10 percent or less by 18
weight coarser than 20 mm then this fraction can be removed without seriously underestimating the strength of the soil. The test is not really suitable for soils or other materials containing more than 10 percent coarser than 20 mm. However, under such circumstances tests on the fraction passing 20 mm carried out at a range of moisture contents will give an indication of whether the material as a whole will lose strength markedly if the moisture content is raised (Croney and Croney 1998).
Figure 2.1: Typical CBR results (Croney and Croney 1998) In most cases the penetration increases, CBR decrease as the penetration increases, so the ratio at the 2.5 mm (0.1 inch) penetration is used as the CBR. In some cases, the ratio at 5 mm (0.2 inch) may be greater than that at 2.5 mm (0.1 inch), and if this occurs, the ratio at 5 mm or 0.2 inch should be used (Huang 1993).
19
2.6.9
Triaxial
Soil strength usually is the resistance developed from a combination of particle rolling, sliding, and crushing and is reduced by any excess pore pressure which develops during particle movement. This resistance to deformation is the shear strength of the soil. Shear strength is measured in terms of two soil parameters, cohesion (c) and angle of internal friction (φ), the resistance to interparticle slip. Detailed description of triaxial test procedures is described by ASTM D 2850, and BS 1377. The first hypothesis
on
the
shear
strength
of
a
soil
was
presented
by
Coulomb
without considering the pore water pressure. Terzaghi pointed out the necessity for considering the effect of pore water pressure on soil strength. Based on reports from Bowels (1979), Hvorslev used laboratory data to verify the use of effective stress parameters to give shear strength equation; s = c′ + σ′n tan φ′
Eq. (2.3)
Where s = shear strength c′ = effective value when σ′ is used. Cohesion is the interparticle attraction effect: it is independent of normal stress but depends considerably on water content and strain rate σ = normal stress on the critical plane: σ′ = σ - u (σ′ = effective stress, u = γw h = pore water, or neutral pressure) φ = angle of internal friction: φ′ = effective angle of internal friction An inspection of Equation (2.3) shows that it is the equation of a straight line which can be plotted tangent to Mohr's circle to represent failure conditions, and from this result, the amount of cohesion (c) as well as friction angle (φ) can be evaluated as shown in Figure 2.2.
20
Figure 2.2: Mohr – Coulomb failure envelope for obtaining the limiting soil shear strength parameters (Bowles 1979)
σ1 and σ3 are deviator stress and all around cell pressure respectively. Shear strength parameters always play a vital role in engineering decision when dealing with any soil including peat. Accuracy in determining the shear strength of soils is associated with several variables namely: origin of soil, water content, organic content, and if the soil is peat, the degree of humification as well (Huat 2004). Also Huat (2005), reports that as the organic content has a negative effect on the shear strength parameters of the soils and as the organic content is increased in soil, its shear strength decreases in return.
Early researches on peat strength indicate some confusion as to whether peat particularly fibric type of peat should be treated as frictional material like mineral soils such as sand or a cohesive soil like clay (Dhowian, and Edil 1980). MacFarlane (1969) describes fibrous peat as a frictional material. Mesri and Ajlouni (2007) state that particle interlocking in fibrous peat is due to the tensile strength of the fibres. On the other hand, loading direction on the fibrous peat has a definitive effect on the peat shear strength parameters.
Mesri and Ajououni (2007) reported some of the finding from Yamaguchi and his colleagues (1985) about triaxial test results on the undisturbed fibrous peat loaded in the direction of the fibres (horizontal) as well as perpendicular to the fibres direction (vertical). Their results indicate that when loads are applied in the direction of the fibres, the friction angle was 35° compared to 51° and 55° 21
when the applied load was vertical. Some values of internal friction angels reported by Bowles 1983, for inorganic soils are presented in Table 2.7. Shear box is the most common test for determining the drained shear strength of fibrous peat, while triaxial test is frequently used for laboratory evaluation of shear strength of peat under consolidated-undrained condition (Noto 1991). Huat (2005b) presented a typical tropical peat list of various types of Malaysian
fibrous, and semi fibrous peat ranging from H1 to H6, showing their cohesion values and internal friction angles found from direct shear tests. The results indicate that maximum cohesion for fibrous and semi fibrous types of peat in various part of Malaysia never goes beyond 17 kPa (Table 2.8). Also Table 2.9 depicts internal friction angels of various types of peat reported by Mesri, and Ajlouni (2007).
Table 2.7: Angle of internal friction (φ) values for various inorganic soils based on triaxial tests (Bowles1983)
22
Table 2.8: Shear strength parameters of various types of organic soil and peat in Malaysia based on laboratory shear box test results (Huat 2005c)
Table 2.9: Friction angles for various types of fibrous peat based on triaxial tests (Mesri and Ajlouni 2007)
As is shown in Table 2.9, the internal friction angle of fibrous peat may reach up to 60°, but this behaviour of fibric peat should not be misleading toward its low shear strength that can reach up to maximum 20 kPa based on many researchers obtained results on the shear strength of peat such as Huat (2004), and Deboucha et al. (2008). Chang et al. (2007), in their research report friction angle of 64.3° (assuming cohesion to be 0 kPa) for Dutch peat having unit weight (γn ) of 1.074 g/cm3. Also a very high φ′ ranging between 60 and 90° was found for Swedish organic gyttja clay with 10% organic content based on report by Larsson (1990). A study by Krieg (2000), and reported by Chang et al. (2007) on the geotechnical properties of various organic clays in Germany with the bulk density varied from 1.2 to 1.5 g/cm3, and organic content of up to 30% shows that values of φ′ ranges from 44° to 74°.
23
Although Edil and Dhowian (1981), in their research state that friction of peat is mostly due to the fibre and the fibre is not always solid, since the fibres are usually filled with water as well as gas. They suggest that, the high friction angle of peat does not actually reflect the high strength of the peat. They also indicate that, as the amount of fibre in the peat is increased the internal friction angle increases as well. On the other hand Mesri and Ajlouni (2007) believe that one of the distinctive characteristic of fibrous peats is their exceptionally high frictional resistance as compared with soft clay and silt deposits. Cheng et al. (2007), concluded that organics soils in general and peat in particular have been found to posses extremely high effective strength parameters, and since this finding is not expected from such soft soils, the phenomenon has yet to be explained, and therefore, the high yield strength value is not to be used in practice.
2.6.10
Consolidation
When any soil is subjected to an increase in pressure (or load), a readjustment in the soil structure occurs which may be considered as consisting primarily of plastic deformation with a corresponding reduction in void ratio. Also, when a saturated soil mass is subjected to a static load increment, the load is usually carried initially by water in the pores because the water is incompressible compared with the soil skeleton. This results in the development of excess pore water pressure (excess pore water pressure is the pressure that exceeds the hydrostatic water pressure). The hydrostatic water pressure is the product of the unit weight of water and the difference in elevation between the given point and the elevation of free water (phreatic surface). As the water drains from the soil pores, the load increment is gradually shifted and transformed to the soil structure. Therefore, it is logical to state that consolidation is the process of gradual transfer of an applied load from the pore water to the soil structure as pore water is squeezed out of the voids. The term consolidation is given when transfer load is accompanied by a change in the total volume of soil equal to the volume of water drained. The amount of water that 24
escapes or drains depends on the size of the load and compressibility of the soil. The rate at which it escapes depends on the coefficient of permeability, thickness, and compressibility of the soil.
In general, the compressibility of a soil consists of three stages, namely initial compression, primary consolidation and secondary compression (creep). While initial compression occurs instantaneously after the application of load, the primary and secondary compressions are time dependent. The initial compression is due partly to the compression of small pockets of gas within the pore spaces, and partly to the elastic compression of soil grains. Primary consolidation is due to dissipation of excess pore water pressure caused by an increase in effective stress whereas secondary compression takes place under constant effective stress after the completion of dissipation of excess pore water pressure. The compressibility behaviors of a soil are usually determined from laboratory one-dimensional consolidation tests. These tests are: Oedometer consolidation test, constant rate of strain (CRS) test, and Rowe Cell. The procedures for these tests are described in, ASTM D 2435, and BS 1377-6. In theses tests, a laterally confined soil is subjected to successively increase vertical pressure, allowing free drainage from the top and/or bottom surfaces (double and single drained).
Consolidation process is true, when saturated cohesive soils undergo loading, because of their relatively low permeability, their compression is controlled by the rate at which water is squeezed out of the pores. Deformation may continue for months, years, or even decades. This is the fundamental and only difference between the compression of granular materials and the consolidation of cohesive soil. Compression of sands occurs almost instantly (immediate settlement), whereas consolidation is a very time dependant process. The difference in settlement rates depends on the difference in permeability (Holtz, and Kovacs 1981). The compressibility of soils is determined by their in-situ void ratio, nature and arrangement of soil particles, and in the case of some soils, chemical bonding (Mesri, and Ajlouni 2007). Consolidation characteristics of soil can be represented by consolidation parameters 25
such as coefficient of compression index (Cc), and recompression index (Cr) or sometimes called swelling index (Cs), coefficient of vertical consolidation (C v), coefficient of secondary compression (Cα), coefficient of compressibility (av), coefficient of volume compressibility (mv) and the preconsolidation pressure (pc). The soil that has been loaded and unloaded will be less compressible when it is reloaded again, thus: settlement will not usually be great when the applied load remains below the pre consolidation pressure. These parameters can be obtained from a complete consolidation test results that includes loading and unloading procedures. The procedure to determine values for C c (Schmertmann method), Cr, and Pc (Casagrande method) from e-log p curve is illustrated in Figure 2.3.
Figure 2.3: procedure of determining Cc, Cr, and Pc from void ratio versus log pressure curve Values of Cc for various types of soils often can also be estimated by empirical formulas provided in the literatures. Although, peat show to have the highest values of up to 15 for Cc, while normally consolidated medium sensitive clays compression indices are often ranges from 0.2 to 0.5. Also the value of Cr sometimes is assumed to be 5 to 10% of Cc (Holtz and Kovacs 1981; Huat 2004). Also compressibility behaviour and ultimate deformation of soft soils can be illustrated by modified compression index (Ccε), and modified recompression index that is also called recompression ratio (Crε). These indices are proportional to the actual settlement of the soft soil, and as these indices tend to increase or decrease, the soil will have more or less settlement respectively. Equations 2.4 and 2.5 are 26
used to evaluate modified compression indices (compression ratios) as well as recompression ratios respectively with eo to be the initial void ratio of the undisturbed soft soil (Holts and Kovacs 1981). Ccε = Cc / (1 + eo)
Eq. (2.4)
Crε = Cr / (1 + eo)
Eq. (2.5)
Where ; Ccε = modified compression index Crε = recompression ratio Cc = compresion index Cr = recompresion index
eo = initial void ratio 2.6.11
Field strength evaluation tests
There are several types of field strength tests that can be used to evaluate the strength of soils, such as standard penetration tests or STP, cone penetration tests or CPT, field vane shear test, and penetrometer tests. Each particular test is set for a different type of soils, for example STP is more suitable for granular soils, while CPT, and vane shear are used for strength estimates of cohesive soils. Also plate load test can be used to estimate load bearing capacity of ground when the soil is not a saturated cohesive soil. A similar test may also be used to evaluate the load bearing capacity of piles that is usually called pile load tests. In the following sections some of the tests that have been used to evaluate strength of peat are discussed with more details.
27
2.6.11.1
Field vane shear test
The vane shear test is a substantially used method to estimate the in-situ undrained shear strength (Su) of very soft, sensitive, fine-grained soil deposits. This method covers the determination in-situ of the shear strength of weak intact cohesive soils using a vane of cruciform section, which is subjected to a torque of sufficient magnitude to shear the soil. The test is suitable for very soft to firm intact saturated cohesive soils [BS 1377 (1998)]. Al-Raziqi and his colleagues (2003) state that field vane shear test decreases either by increasing the water content or by increasing the percentage of organic content of soils.
Huat (2004) estimates of peat shear strength obtained from field vane shear ranges from 3 to 15 kPa. Researches done by Al-Raziqi et al. (2003) and Huat (2004) indicate that as the peat become more decomposed their vane shear strengths decrease. Based on their research, among various types of peat (H1 to H10) in Malaysia, the vane shear strengths are below 20 kPa and these values belong to H2-H5 group of peat.
Another in-situ test that is usually used to evaluate the shear strength of soft ground such as peat deposits is field pressuremeter test. From the plot of volume change versus the pressure, shear strength of the soil can be estimated. Obtained results from pressuremeter tests for tropical peat located in Malaysia reported by Ting et al. (2005) show that, their strength ranges between 3 to 8 kPa.
2.6.11.2
Plate load test
Plate load test actually is a model footing test, and is used to estimate the compressibility and bearing capacity of ground. The test is usually performed for the determination of bearing capacity of soils for allowable settlement under static loads at shallow foundation. This test is the method of conducting the 28
load test on soils and evaluation of bearing capacities and settlement from the test. This method covers the determination of the vertical deformation and strength characteristics of soil in-situ by assessing the force and amount of penetration with time when a rigid plate is made to penetrate the soil [BS 1377 (1998)]. Load bearing capacity of the soil can be estimated based on a graph that is plotted with the mean settlement versus bearing pressure. Some researchers such as Black et al. (2007) used this type of test to evaluate the load bearing capacity of reinforced columns within weak soil deposits (peat) in laboratory scaled test box. In the case of soft soils, and if bearing capacity failure is not apparent from the load-settlement curve, it is assumed to be the load at which settlement equals 15% of plate diameter. 2.6.12
pH
This test describes the procedure for determining the pH value, by the electrometric method, which gives a direct reading of the pH value of a soil suspension in water. Standard description of pH test is presented by ASTM D 4972-01, as well as BS 1377. In general, pH is a measure of the acidity or alkalinity of water and relates to the concentration of hydrogen ions. A pH of 7.0 is neutral, below 7.0 is acidic, and above 7.0 is alkaline. Electro chemical classification tests such as pH, resistivity, sulphate ion content, sulphides, and chloride ion content provide the geotechnical specialist with quantitative information related to the aggressiveness of the soil conditions. (US. Dept. of Transportation 2006). The organic soils in general and peat in particular are acidic and the pH values are between 3.0 - 4.5. Ombrogenous peat which is essentially a pile-up of loose trunks, branches, roots and fruits, is reported to be characterized by a low pH (Mutallib et al. 1991).
Swedish Dömle peat, with natural water content of 2000 %, specific gravity of 1.44, and organic content of 97% is reported to have a pH of 4.3 (Åhnberg 2006). pH test is also used to determine the 29
optimum dosage rate of lime treated clay soil. In, Thompson Procedure as well as Eades and Grim Procedure, the optimum lime content is first estimated by measuring the pH of several soil lime mixtures with varying lime contents. The lowest lime content that provides a pH of 12.4 is then used as the starting point for determining the optimum lime content (Geiman 2005; Little 1999). One of the reasons to affect the stabilization of organic soils in general and peat in particular is their lower pH values, beside their high organic contents which make them harder to stabilize compared with inorganic soils. (Mosely and Kirsch 2004; Janz and Johansson 2002).
2.6.13
Scanning electron microscopy (SEM)
This test is a type of electron microscope that images the sample surface by scanning it with a highenergy beam of electrons. This test is usually used to evaluate the morphology and microstructure of various substances. In this test fine focused electron beam of about 10-2 mm are released toward an element of a substance, and an image will be the result of this test that depict a close physical characters as well as any possible structural bounding of the particles consisting that element. Sometimes, the test is being referred to as scanning electron microphotograph as well. Figure 2.4 (a, and b) shows, the typical fibre orientation obtained by scanning electron microscope for Middleton fibrous peat. The samples were cut in vertical and horizontal sections to enable the observation of the
rearrangement of the fibres. Comparison of the two images indicates a pronounced structural anisotropy for the fibrous peat with the void spaces in the horizontal direction larger than those in the vertical direction resulting from the fibre orientation within the soil (Gofar 2006; Fox and Edil 1996).
30
Figure 2.4: SEM images of fibrous peat samples at initial state, a) horizontal section b) vertical section (Gofar 2006) 2.6.14
Energy dispersing x – ray analysis (EDXA)
This test is an analytical technique used for the chemical characterization of a sample. As a type of spectroscopy, it relies on the investigation of a sample through interactions between electromagnetic radiation and matter, analyzing x-rays emitted by the matter in response to being hit with charged particles. Its characterization capabilities are due in large part to the fundamental principle that each element has a unique atomic structure allowing x-rays that are characteristic of an element's atomic structure to be identified uniquely from each other. In this technique, electrons are bombarded in the area of desired elemental composition. The elements present will emit characteristics x-rays, which were then recorded on a detector (Vasudev 2007). The result of this test can reveal the chemical compound of various binding agents (e.g. cement or lime) and chemical additives such as micro silica, blast furnace slag, or fly ash before and after peat treatment as well.
31
2.6.15
Field sample collections
The purpose of a sampling program is to obtain samples that reasonably represent subsurface conditions. Soil samples are normally divided into two classes, which are undisturbed and disturbed samples. BS 1377 (1990) describes subsurface investigation as well as sampling procedures. Huat, and Ali (2007), define disturbed sample as a sample whose structure has been totally or partially disturbed or destroyed. Usually, disturbed samples can be obtained by using hand augers or from test pits. Most literature review agree that, in reality, it is impossible to retrieve truly undisturbed samples since changes in the state of stress in the sample occur upon sampling and removal of the sample from depth (Huat, and Ali 2007; U.S. Dept. of Transportation 2006). However the goal of high-quality undisturbed sampling is to minimize the potential for; (1) alteration of the soil structure (2) changes in moisture content or void ratio: and (3) changes in chemical composition of the soil (U.S. Dept. of Transportation 2006). Samples obtained from the site either, disturbed or undisturbed should represent the in-situ conditions of the soil. Undisturbed sampling equipments which are mostly cylindrical are to have thin walled, that they can cut through the soil deposit as the samples slide inside them. As the samplers are larger in diameter, the obtained soil samples are more undisturbed.
Usually, the area ratio (AR) and the inside clearance ratio (ICR) of cylindrical samplers are parameters that are used to evaluate the disturbance potential for different types of soil samplers. These parameters are defined as follows: AR (%) = [(Do2 – Di2) / (Di2) ] × 100
Eq. (2.6)
ICR (%) = [(Di) – (De) / (De) ] × 100
Eq. (2.7)
Where De = diameter at the sampler cutting tip (edge), Di = inside diameter of the sampling tube, and Do = outside diameter of the sampling tube. For a sample to be considered undisturbed, the ICR should 32
be approximately 1 percent and the AR should be 10 percent or less. Thin-walled tubes such as Shelby tubes shown in Figure 2.5, are typically manufactured to meet these specifications (Huat and Ali 2007; U.S. Dept. of Transportation 2006).
Figure 2.5: Schematic of thin-walled (Shelby) tube and photo of tube with end caps (U.S. Dept. of Transportation 2006) Duraisamy et al. (2007, 2009) designed and fabricated a hand auger (UPM sampler) to collect undisturbed peat samples as shown in Figure 2.6. The sampler fulfils the requirements for undisturbed sampler’s specification as far as %AR and %ICR (equations 2.6, and 2.7) are concerned.
33
Figure 2.6: UPM peat sampler (Duraisamy et al. 2009)
2.7
Soft ground improvement
In general, a soil exhibiting a marked resistance to deformation under imposed load, or continuing load application, whether in wet or dry condition, is said to be a stable soil. When a less stable soil is treated to improve its strength and its resistance to change, it is said to be stabilized. Therefore ground improvement or stabilization infers improvement in strength, stiffness, and durability. Usually, when the soils at a site are loose, or highly compressible, or when they have undesirable engineering properties, making them suitable for use in a construction project, they may have to be stabilized. A significant increase in bearing capacity may be achieved by altering the soil properties of φ, cohesion (c), and the unit weight γ. Settlements may be reduced by increasing the density with the resulting decrease in void ratio from particle packing. Stabilization may consist of any or a combination of the followings list methods (Smoltczyk 2003; Woods et al. 1960; Bowles 1979; Bowles 1988; Huat and Ali 2007; Lee et al. 1983; and Murthy 2003): 34
a) Compaction b) Blasting c) Chemical treatment of the weak soil d) Grouting e) Deep dynamic compaction f) Use of geotextiles g) Sand and stone columns h) Use of Electro-Osmosis i) Thermal (freezing or heating) treatment j) Vibro-replacement stone columns k) Mixing the weak soil with a better quality soils l) Bypassing the weak soil and transferring the load to a more stable soil layer m) Lowering the water table (drainage) n) Removal and replacing the weak soil o) Preloading or surcharging the soft soil area
The selection of the most suitable ground improvement or stabilization method accompanied by the appropriate process sequences for any specific application
must always be based on a through
technical study such as, loading conditions, soil type, surface area and volume of the ground to be improved, and economical comparison (Smoltczyk 2003; Huat 2005). 2.7.1
Binding agents
The physical properties of weak soils can often economically be improved by the use of bindings materials. Some of the more widely used admixtures include Portland cement, lime and asphalt. According to AASHTO designation M145-82, cement can be used to strengthen A-1 to A-8 soils, and 35
as the soil particles are decreased more cement will be needed to be more effective (Croney and Croney 1998). Other chemical agents that some times used to stabilize certain types of soils are: sodium chloride, calcium chloride, and paper mill wastes (Bowels 1979). In the following section cement is being discussed with further details. 2.7.1.1
Cement
Cement is defined as adhesive substances capable of uniting fragment or masses of solid matter to a compact whole. Portland cement (PC) clinker is produced by calcining a mixture of finely ground limestone and clay in an inclined rotary kiln to a maximum temperature of 1450°C, with a surface area of around 300 m2/kg, specific gravity 3.15, and bulk density of 1350 kg/m3 (YTL cement 2008). After cooling, the clinker is grounded with 2-5% gypsum to control the rate of setting during addition of water. Table 2.10 shows the main components as well as chemical compositions of ordinary Portland concrete (OPC). Table 2.11 presents various types of Portland cement as well as their particular uses. Table 2.10: Main components and chemical compositions of ordinary Portland cement (Neville 1999; Janz and Johanson 2002; Chen 2008)
36
Table 2.11: Portland cement types and their uses (U.S. Dept. of Transportation 1999; Taylor and Thomas 1997)
2.7.2
Additives
Kett (2000), defines additives for concrete as materials other than water, aggregates (gravel, and sand), and hydraulic cement that are added to the mixture before or during the mixing procedure. Various types of additives that are usually used in concrete mixtures improve the bounding between the aggregate particles, and giving the product more strength to carry loads or making it more durable. The additives may be chemically active, and react with the cement and water present in the mixture, and therefore making stronger bounds, or none chemically active materials that simply add to the particle bindings by their physical shapes, and not of their chemical substances. Generally chemically active materials either are soluble or decomposable in water while on the other hand none chemically active materials do not dissolve in water. Certain chemical additives are sometimes added to soil-cement with the purpose either to reduce the cement consumption or to make a soil suitable for stabilization which is not responsive to cement alone in its natural state (Punmia 2005). Literature review reveals that, some types of chemically active additives such as ground granulated blast furnace slag, and fly ash have been tried in conjunction with cement to further improve the engineering behaviour of peat under load, however literature review on the use of micro silica (chemically active), polypropylene fibres, and steel fibres (non chemically actives) as additives are
37
limited to their use in concrete mixtures. Polypropylene also has been used to reinforce mineral soils as well. In the following sections, each of these additives and their use is discussed in more detail. 2.7.2.1
Ground granulated blast furnace slag (GGBS)
Ground granulated blast-furnace slag is the granular pozzolanic material formed when molten iron blast furnace slag is rapidly chilled (quenched) by immersion in water. It is a granular product with very limited crystal formation, is highly cementitious in nature and, ground to cement fineness, and hydrates like Portland cement with a specific surface around 450 m2/g, specific gravity of 2.9, and bulk density of 1150 kg/m3 (Fernandez and Puertaz 1997; YTL cement 2008). Ground blast slag used as stabilizer has latent hydraulic properties. This means that, like pozzolanic materials, the slag can form strengthenhancing products with calcium hydroxide (Ca(OH)2)[Axelsson et al. 2002]. As it was mentioned earlier, blast furnace slag is considered to be a latent hydraulic material that means it needs an activator such as calcium hydroxide to react. Its reactivity also depends on the CaO/SiO 2 ratio. As this ratio is increased, the more the hydraulic material will be. CaO/SiO2 ratio for blast furnace slag is about 1, while it is up to 3 for ordinary Portland cement. Hydraulic materials such as OPC react spontaneously with water. Since reaction produced by blast furnace slag is slower than OPC, therefore gives a slower strength gain and lower heat evaporation than with cement. However, the long term strength of slag admixture can be higher (Axelsson et al. 2002; Janz and Johansson 2002). 2.7.2.2
Pulverized-Fuel ash or PFA (Fly ash)
Pulverised-Fuel ash, also known as fly ash, is the fine residue produced when hard or bituminous coal is burnt in power station. Because of variations in coals from different sources, as well as differences in the design of coal-fired boilers, not all fly ash is the same having similar properties.
38
Black coal gives a fly ash with lower CaO content than brown coal, but different black coal and brown coal gives a fly ash with lower CaO content than brown coal, but different black coals and brown coals also may vary widely. Thus a change in the in the coal burnt by a power station can result in a fly ash with entirely different properties.
In order for a pozzolanic material such as fly ash to react with water at all an external source of lime is necessary, e.g. in the form of Portland cement. When cement reacts with water they form calcium hydroxide Ca(OH)2, which in turn may form either a strength enhancing CSH gel of the same type as Portland cement but with a lower CaO/SiO 2 ratio, or calcium aluminate silicate hydrate (CASH), which is closely similar to CSH but contains aluminium (Janz, and Johansson 2002;).
Fly ash to be used in combination with Portland cement has been classified by ASTM C 618 into two classes, F and C, based on the chemical composition of the fly ash. The most influencing factor that divide these two classes of fly ashes are their amount of calcium, silica (SiO2), alumina (Al2O3), and iron contents (Fe2O3) among other factors. Some of the most influential parameters that divide the two types of flay ashes are shown in Table 2.12.
39
Table 2.12: Influencing parameters to classify fly ash (Samsuri 1997)
Past researches show that addition of fly ash in cement, or lime when mixed with mineral soils can improve the performance of the final product (Sukumar et al. 2008; Douglas 2004; Sobhan, and Mashnad 2002; Little 1999).
2.7.2.3
Silica fume or micro silica
Silica fume or micro silica is an extremely fine product of high amorphous silica content arising from the condensation of rising vapour given off in the manufacture of ferrosilicon and metallic silicon in high temperature electric arc furnaces. Silica fume is extremely fine and dusty, with a typical particle size equal to 1.016 x 10-4 mm and having surface area around 19000 m2/kg. Its pozzolanic activity with cement is estimated at 120-200%. Cement and silica fume mix show a higher strength. Silica fume is said to be a very effective pozzolanic as well as siliceous material, which in itself possesses little or no cementitious property, but in finely divided form and in the presence of moisture, it will chemically react with calcium hydroxide to form compounds possessing cementitious properties (Agarwal 2006).
40
Silica fume as a pozzolanic additive gives cement increased strength, density, and durability (Fleri, and Whetstone 2007).
There are limited available literature on cement, silica fume, and peat. Although silica fume is used as an additive to produce high performance concrete. High performance concrete is more homogeneous than normal strength concrete, and if made with small aggregates it can be compared to a strong rock. One of the benefits of using silica fume in Portland cement-based composites is its performance as filler in capillary pores and the cement past-aggregate interface (Toutanj and El-Korchi 1999). Detwiler and Metha (1989) had observed that cement reacts with water to form calcium silicate hydrate and calcium hydroxide. Silica fume reacts with the calcium hydroxide in presence of water to form calcium silicate hydrate. The increased calcium silicate hydrate gel and reduction in capillary pores in the cement paste are the main factors in its increased strength and impermeability. Silica fume and fly ash undergoes the same type of pozzolanic reaction. The strength gain is more rapid than fly ash but slower than that of cement. The pozzolanic reaction is highly temperature dependant, so that the short term strength is lower at low temperatures. However, long term strength is increased by replacing part of the cement with silica fume (Janz and Johansson, 2002). Some of the physical properties of silica fume are shown in Tables 2.13.
Table 2.13: Physical Properties of silica fume (Toutanji et al. 1997)
The usual dosage of silica fume used along with cement in concrete mixtures is 5 to 10% by weight of cement (Bunke, 1988). Hooton (1993) has observed that addition of 15 and 20% of silica fume 41
decreases tensile strength of 91 days old concrete by 15 and 20% respectively. Toutanji et al. (1999) shows that partial replacement of cement by 8% of silica fume resulted in an increase in tensile strength of cement mortar (cement, and sand). The replacement of cement by higher dosage of silica fume (16, 25%) resulted in a decrease in the tensile strength of mortar. 2.7.2.4
Polypropylene fibres (PPF)
Polypropylene (PP) is a versatile thermoplastic material, which is produced by polymerizing monomer units of polypropylene molecules into very long polymer molecules or chains in the presence of a catalyst under carefully, controlled heat and pressure. It has a good combination of properties, cheaper than many other materials that belong to the family of polyolefins and it can be manufactured using various techniques. In general, polypropylene (Figure 2.7) is resistant to alcohols, organic acids, esters and ketones. Its general use in construction industry is to reinforce concrete to control cracks as well as for increasing their load bearing capacity and durability (Mulli et al. 2006). Some properties of polypropylene fibres are listed in Table 2.14. Polypropylene fibres also has been used successfully as none chemically admixture to strengthen various types of soils such as sands and clays in conjunction with a binding agent such as Portland cement and or lime (Brown et al. 2002; Sobhan and Mashnad 2002; Kaniraj and Gayathri 2003; and Tang et al. 2007).
Studies have also been carried out by several researchers (Gray and Ohashi 1983; Maher and Gray 1990; Consoili et al. 2007b and 2007c; Yetimoglu and Salbas 200; Yetimoglu et al. 2005; Ranjan et al. 1996; Park and Tan 2005; Tang et al. 2007; Chauhan et al. 2008; and Sivakumar et al. 2008) to study the influence of fibre inclusion on the mechanical behaviour of cemented soil. In general, reports in the literature show that randomly distributed fibres can be used to overcome the drawback of using cement alone such as high stiffness and brittle behaviour of the stabilized soil. In a series of laboratory unconfined compressive strength tests on, the raw specimens attained a distinct axial failure stress at an 42
axial strain of about 1.5 – 2.5% following which they collapsed. But, the fibre-reinforced specimens exhibited a highly ductile behaviour (Kaniraj and Gayathri 2003). Also, from the experiments on field test sections in which a sandy soil was stabilized with polypropylene fibres, Santoni and Webster (2001) concluded that the technique showed great potential for military airfield and road applications and that a 203 mm thick sand fibre layer was sufficient to support substantial amounts of military truck traffic.
a)
b)
Figure 2.7: Polypropylene fibres: a) SEM image [Kaniraj and Gayathri 2003], b) Photograph showing the discrete short PP- fibre (Chaosheng et. al 2007) According to Tang et al. (2007), in fibre reinforced soils the fibre surface is attached by many soil particles which make the contribution to bond strength and friction between the fibre and soil matrix. The distributed discrete fibres act as a spatial three dimensional network to interlock soil grains, help grains to form a unitary coherent matrix and restrict the displacement. Consequently, the stretching resistance between soil particles and strength behaviour is improved. Because of the interfacial force, the fibres in the matrix are difficult to slide and they can bear tensile stress, as the sketch drawing shown in Figure 2.8. 43
Figure 2.8: Sketch of mechanical behaviour at the interface between fibre surface and soil matrix (Tang et al. 2007) Table 2.14: Polypropylene fibres specifications (Sika fibres 2005; and Brown et al. 2002)
The minimum dosage rate of PPF recommended for concrete mixes starts with 0.6 kg/m3 (Sika fibres 2005, and The Fibre Depot 2005). Also, Tang et al. (2007) tried 0.05, 0.15, and 0.25 % (by soil’s weight) of polypropylene fibres (PPF) through UCS tests to find the optimum PPF amount to strengthen cement treated clay soil. 2.7.2.5
Steel fibres
Steel fibres are made of cold drawn steel wire with low content of carbon (C) or stainless steel wire. Steel fibres are manufactured in different types; hooked, undulated or flat, according to the construction project. These fibres are used in construction, for concrete reinforcement. They are mostly used for reinforcement of concrete, mortar and other composite materials. Steel fibre reinforcement products are 44
designed to increase concrete material performance in a variety of applications. Technical advantages of steel fibres in concrete include: improve flexural toughness, increase fatigue, enhance impact and abrasion resistance, additional load bearing capacity, controlled shrinkage behaviour, increase durability. Steel fibres can also be used as an addition or total replacement for conventional steel meshes (Adams 1991; http://www.steelfibre.org). Figure 2.9 shows, schematic performances of two different concrete blocks upon loadings, plain concrete as well as fibre reinforced concrete (FRC). Also, Figure 2.10 shows the hooked end shape of steel fibres that are most often used to strengthen concrete mixes, and Table 2.15 shows steel fibres usual properties as well. a)
b)
Figure 2.9: Schematic diagram of concrete blocks performances under load a) plain concrete and b) Steel fibres reinforced concrete (Timuran Engineering 2007) a)
b)
Figure 2.10: Hooked end steel fibres a) dimensions, b) photograph (Timuran Engineering 2007) Table 2.15: Hooked steel fibres specifications (Timuran Engineering 2007)
45
2.7.3
Cementitious mechanism in soil stabilization
Portland cement is a binding agent, and when mixed with water initiates a chemical process that is called hydration which forms hard cement past and it binds and strengthens the soil without the need to add an activator. It consists of numerous minerals, and when mixed with water it forms calcium silicate hydrate and calcium hydroxide Ca (OH)2. Calcium silicate hydrate, generally referred to as CSH gel, forms on the surfaces of the cement particles and because it has a strongly cementing effect, it binds the soil together and increases its strength (Axelsson et al. 2002).
Latent hydraulic materials have to be activated with e.g. calcium hydroxide in order to react, while pozzolanic materials require the availability of calcium hydroxide throughout the reaction process. The reactivity of cement, latent hydraulic and pozzolanic materials depends among other things on the ratio of lime to silica, CaO/SiO2. The larger this ratio is, the more hydraulic is the material (Janz, and Johanson 2002). Table 2.16 summarises the strength-enhancing reactions of cement, granulated blast furnace slag, fly ash, and silica fume. Table 2.16: Strength enhancing reactions for Portland cements and chemical additives (Janz and Johanson 2002)
The pozzolanic reaction is slow and is slowed further by the formation of a shell of calcium silicate hydrate (CSH) gel around the pozzolanic particles such as fly ash. The strength gain then is very slow but effect of pozzolanic reaction on long term strength can be considerable. Also pozzolanic materials 46
require the availability of calcium hydroxide through out the reaction process (Axelsson et al. 2002; Janz, and Johansson 2002). The reaction rate of the hydraulic, latent hydraulic and pozzolanic materials is mostly dependent on the particle size. As the specific surface is higher, more rate of rapid reaction occurs (Janz, and Johanson 2002). 2.7.3.1
Factors affecting cement treated peat
Peat contain significant amount of organic matter, some of which are complex aromatic macromolecules collectively known as humic substance, that contribute to odour, taste, as well as acidity in water supply (Fong and Mohamed 2006). Humic substances are a complex series of relatively high molecular weight, organic substances that are formed by secondary synthesis reactions in soils. They represent one of the most chemically reactive fractions of the soil due to their high surface area, and surface charge, and thus have a critical influence on the chemical and physical properties of soils. Their role might be compared to that of clay fraction in inorganic soils (Santagata et al. 2008). It is generally recognized that organic matter and low pH of peat in the presence of black humic acid tend to interfere the hydration process, if it is to be stabilized by ordinary Portland cement. This is possible due to the fact that the acid tends to react with calcium liberated from cement hydrolysis to form insoluble calcium humic acid making it difficult for calcium crystallization, which is responsible for the increase of cement soil strength to take place (Hashim and Islam 2008a; Chen and Wang 2005).
Peat usually requires larger stabilizer quantities, because they contain few solids to stabilize, and therefore more stabilizers is needed to bind the particles together. Peat also has much higher porosity and water: soil ratio. The high water content gives a higher water/total-cementitious ratio and hence the lower strength. The quantity of binder for soils with high organic content must exceed a certain threshold before any stabilization is obtained. A possible reason for this threshold effect may be that 47
sufficient binder must be added to neutralize the humic acids (Janz and Johansson 2002). Based on the literature review, it is possible to conclude that, there are two influencing factors affecting stabilization process of peat among others; first high humic acid content, and second high water content of peat. Other factors that affect the outcome of the stabilization process include; quantity of cement as the binder, type of additives, curing type, and curing periods. For mass soil stabilization, Croney and Croney (1998) state that, there is no doubt that the mixture of cement with soil which is free of deleterious matter (e.g. organic or acidic substances) will increase the strength and render the soil more capable of carrying construction traffic. 2.8
Traditional curing types for cement treated peat
Literature review on curing procedures, on cement treated peat indicates that, almost all of the stabilized peat samples prepared in laboratory were cured by two types traditional curing methods namely; moist curing, and moist curing with surcharge loads. In moist curing technique, the cement treated peat samples were partially or completely submerged in water during curing periods, and in moist curing with surcharge loads, samples were subjected to a surcharge loads of equal to field effective overburden pressure on them while partially or completely submerged in water during curing periods. 2.9
Peat stabilization
Stabilization, in a broad sense, incorporates the various methods employed for modifying the properties of weak soils to improve their engineering performance. The most common application of soil stabilization may include construction of road and air field pavements, and light weight family house, where the main objective is to increase the stability of the poor soil and to reduce the construction cost by making best use of the locally available material. 48
All three types of peat deposits; fibric, hemic, and sapric are considered very weak, and problematic as far as their loads bearing capacities are concerned. American association state highway transportation officials or AASHTO soil classification designates peat as A-8 and describes it as peat, muck, humus, or swamp soil ordinary found in obvious unstable swampy areas, and characterizes it by its low density, high compressibility, high water content, and high organic content (Wood et al. 1960). Holtz and Kovacs (1981) consider peat as one of the softest soils, with very low bearing capacity and low CBR values of less than 2%. Kentucky Transportation Cabinet (2007) recommends a CBR of 1% for peat, to be considered when designing for the pavement. Literature review for their shear strength reveals that, fibrous peats have the highest shear strength among various type of peat, however no report of shear strength more than 20 kPa for peat is been published ( Huat 2004, 2007; Deboucha et al. 2008). Considering fibric peat having 20 kPa shear strength, and with a CBR of less than 2%, it is still far less than to be closer to a less problematic or stable soil. Since peat in general and fibrous peat in particular, are unstable upon being loaded, they need to be stabilized or their engineering properties have to be improved either for line constructions or to support other light structures such as low height family housings.
When line constructions are concerned, at values of CBR below 2%, the soft subgrade may not be able to support construction of foundation layer, and therefore subgrade improvement is required (Hunter 2000). As an example, a flexible or asphalt type of pavement designed to carry 100 million standard axles would need to have a thickness of about 950 mm of granular subbase, if the subgrade had a CBR value of 1 percent, the thickness can be reduced significantly if the soil is of type which can be treated by addition of a small amount of cement (increasing CBR of 1% to 10% reduces the granular thickness of subbase from 950 to 500mm) [Vorobieff and Murphy 2003].
49
The most usual methods among engineers so far to deal with any type of peat deposits have been either to remove the peat and replace it with suitable soil or to pass piles through it to the stronger soil layers below. On the other hand, research has been carried out to discover ways to strengthen peat deposits. These methods include, peat stabilisation using a mixture of various binders such as cement, and different admixtures such as fly ash and blast furnace slag. Also, the behaviour of the peat has been improved by stabilisation techniques where the binders are mixed with the in-situ peat to create columnar reinforcement in peat ground. Some of the researches done in regards to peat stabilization in general, and to make fibrous peat more stable in particular include the followings.
Axelsson et al. (2002), in their laboratory research used several types of admixtures to stabilize fibrous peat in laboratory. They used unconfined compressive strength tests to evaluate the results for 28 days of cured samples. Their findings include:
The curing method used for their research was partially moist curing method with the bottom part of the samples exposed to water with 18 kPa surcharge load during the curing period. Their overall, final results indicate that the best result was obtained with mixture of OPC, blast slag and fibrous peat (H1 – H3) samples, and next to the best was with cement only mixed with peat, and the worst was obtained with cement and flay ash mixed with peat. The results also indicate that, the quantity of the binder needs to exceed a threshold in order for the peat to begin to be stabilized, and they suggest a minimum of 150 kg/m3 of stabilizer to be used for strengthening peat. A possible reason for this phenomenon
50
may be the existence of humic acid in peat, which needs to be neutralized first before stabilization process to take effect.
Hebbib, and Farrell (2003) research on fibrous peat (H2) stabilization with different dosage ratios of admixtures; OPC, GGBS, fly ash, lime, and gypsum. They used moist curing technique with 18 kPa surcharge load to cure samples during 28 days of curing period. Unconfined compressive strength was their strength evaluation test. The results of their study for various types of stabilized samples include the followings;
The results presented above indicate that ordinary Portland cement is most effective when is used alone, and also the worst combination belongs to blast furnace slag and gypsum is used in the mixtures. They recommend a minimum quantity for the stabilizer to be at least 150 kg/m3 in order for the strengthening to occur. Also their findings indicate that preloading of the stabilized peat immediately after mixing plays a fundamental role in the mechanical behaviour of the stabilized peat achieved. Higher strength is achieved when the stabilized peat is preloaded, or the amount of OPC is increased. Alwi (2007), in his research used OPC, along with bentonite, blast furnace slag, and sand with various dosage ratios to stabilize semi fibrous peat (H4-H6). He used moist curing technique with 10 kPa surcharge load to cure samples during 7, and 56 days of curing periods. Unconfined compressive
51
strength was the strength evaluation test for the samples. The results of his study for various types of stabilized samples include the followings;
According to the obtained results shown, the unconfined compressive strength of stabilized materials formed by peat, cement, sand, and sodium bentonite is the highest value among various types of samples, and that is because sands in peat acts as a filler to strengthen the peat structure as well as a material that is bounded by cementitious reaction of cement, and bentonite. Also based on his results, the use of admixture less than 200 kg/m3 did not significantly improve the compressive strength of stabilized peat without sand.
Wong et al. (2008b) studied the effect of various admixtures with fibrous peat (H4) by means of unconfined compressive strength. They used 300 kg/m3 of OPC in each mixture, while moist curing them along with 100 kPa for 7 days. The UCS values as well as different type of mixture dosages in their research include;
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The results shown indicate that when insufficient cement was added to stabilize peat, provision of tricalcium silicate to neutralize humic acid was inadequate to induce cement hydration. Also the more sand added to the peat admixture, the more solid particles were present and the more cementation bonds were formed at the contact points between the solid particles, thus interlocking the organic and soil particles in peat to form stabilized peat structure.
Hashim, and Islam (2008a), conducted a series of unconfined compressive strength tests on stabilized fibrous peat samples mixed with a dosage rate of 350 kg/m3, with 85% OPC, and 15% bentonite by weight, as well as 25% sand (by volume). They reported the strength increase of the stabilized samples in 1, 3, 7, and 28 days curing periods, and concluded that as the curing time is increased the stabilized peat samples gain strength as well as is shown;
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Black et al. (2007) conducted plate load tests on different types of columns (L = 720 mm, and D = 80 mm) made of granular materials and granular column with tubular wire mesh as well as on untreated peat layer in a laboratory modelled test box. They used a layer of peat sandwiched between two sand layers, with a thickness of 240 mm for each layer with a total thickness of 720 mm. The plate load test results indicate that for 10 mm settlement, the load increased from 0.8 to 1.2 and 1.5 kN for untreated, granular, and jacketed granular column respectively. This indicates that load bearing capacity of the untreated ground with peat can be improved through deep stabilizations and use of columns made of either plain granular materials or when wrapped in wire mesh.
Also, Hebib and Farrell (2003) provide a technique of surface stabilization of fibrous peat (H2) with cement in combination with stabilized cement treated peat columns (a combination of surface layer with 500 mm thickness and deep stabilization with 1500 mm height column) for foundation load support, and tested the system using a large chamber box. The formation of the stabilized soil structure (surface and deep) within the testing chamber significantly reduced the amount of settlement when compared with that interpreted for the untreated soil, and the rate of consolidation was accelerated as well. Their result indicates that the final settlement in the cement treated peat inside the chamber box (imposed by identical loads) was reduced by a factor of 0.28 compared to the case where the peat was untreated.
Duraisamy et al. (2007, and 2009) studied the compressibility behaviour of cement columns in fibrous peat. They used 100% cement columns poured in to the predrilled holes made in undisturbed fibrous peat, and used Rowe cell consolidation apparatus to measure the coefficient of compression (Cc), and coefficient of secondary compression index (Cα). They used moist curing technique for 28 days to cure the cement columns. The results obtained from this research indicate that compression index, as well as secondary compression index are significantly reduced by close to 50%, when cement column with D = 54
45 mm, and L = 50 mm was used. When the size of the columns diameter was increased to 50 mm, the reduction of the indices reached to 80% compared with the plain fibrous peat.
Kazemian and Huat (2009), used Rowe cell consolidation tests to investigate the variation of coefficient of compression (Cc), as well as evaluating the law of compressibility (Cα/Cc) for fibrous peat at its natural state, as well as with different dosage ratios of cement treated columns reinforcing fibrous peat. They prepared mixtures of fibrous peat with various amounts of cement and then inserted in to a predrilled hole at the centre of undisturbed fibrous peat samples. Columns size was 45 mm in diameter, and 50 mm in length. Moist curing technique was used to cure the cement treated peat columns during curing period. The results of their study indicate that, cement treated peat columns have reduced Cc, by the followings;
A comparison between Duraisamy et al. (2007, 2009) method using 100% cement columns, and Kazemian and Huat (2009) procedure of using partially cement treated columns in fibric peat show that as the cement amounts in columns are increased, the values of compression coefficients are decreased further. This indicates that cement used in peat columns does improve the compressibility behaviours of fibrous peat due to imposed loading.
Simple method of drainage was used by Rahman et al. (2004) in their laboratory study. Their analysis shows that peat gains strength upon drainage and therefore reducing moisture contents can increase the
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shear strength of plain peat. The measured shear strength parameters of the drained peat for various samples were increased up to 35% using direct shear box apparatus.
McManus et al. (1997) recommend the following options when constructing on peat, depending on the thickness of the deposits. • Removal and Replacement when the thickness of the deposit is 3 m. • When the thickness of the deposit is more than 3 m but less than 10 m, the following options may be considered: preloading, stage construction with vertical and sand drains, lightweight fills and surface mattresses. • For deposits of greater than 10 m, one of the deep stabilization techniques, including the pile support method can be considered. According to Huat (2004), in evaluating the effectiveness of the various construction techniques on peat for line constructions such as roads, many variables need to be considered including; effectiveness of the method, availability of materials and equipment, cost of materials, construction maintenance, and environmental effects. 2.10
Conclusions
From literature reviews, it is possible to observe that fibrous peat is a very soft and unstable type of soil, and since it is a highly organic (more than 75% organic content) it is more difficult to stabilize it compared with mineral soils. Peat and organic soils need more stabilizers agent such as cement to obtain the same degree of strength compared with inorganic soils. Results from researchers show that various types of binding agents such as cement, lime, or gypsum have been used in laboratories to stabilize various types peats.
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Chemically active additives such as blast furnace slag, fly ash, sodium bentonite, or sodium chlorides have also been used alone or in combination with cement to strengthen fibrous peat. Some researchers used sands as reinforcement and fillers agent to cement treated fibrous peat as well. In general, and based on the results of researchers on peat stabilizations, among the stabilizers that have been used, to strengthen fibrous peat, cement has shown the highest effectiveness compared with other stabilizers such as blast furnace slag, when used alone or when used with blast furnace slag, and also when sands are added to mixtures to improve fibrous peat stabilities. Also, Present of fly ash in the mixture of cement seems to be less effective to increase the strength of fibrous peat compared with blast furnace slag. Literature review show that the use of none chemically active additives such as polypropylene fibres or steel fibres are limited to concrete mixtures, while random distribution of polypropylene fibres has shown good degrees of success to increase the stability of clayey soils which is also considered to be an inorganic type soft soil when saturated. According to past studies on peat, there are limited studies are available for silica fume as an additive to be used with cement treated peat. Curing types of organic soils and peat, which have been widely used by researches, are; moist curing and moist curing with surcharge load, while use of air curing technique has been limited to inorganic soils. Literature reviews indicate that, among researchers the most usual tests to evaluate the strength and compressibility behaviours of untreated as well as stabilized peat samples in the laboratory are unconfined compressive strength (UCS), and Rowe cell consolidation tests respectively. Also, plate load test which is a model footing test has been used by some researchers to evaluate load bearing capacity as well as deformation of untreated as well as treated peat deposits as well.
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From literature reviews, it is observed that the most influencing factors in stabilizing highly organic soils containing more than 75% organic contents such as fibrous peat in the laboratory include; type and amount of stabilizers, curing types as well as curing periods.
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CHAPTER 3
METHODOLOGY
3.1
Introduction
An experimental program was planned, and designed to evaluate the engineering behaviours of undisturbed (untreated) as well as treated fibrous peat (peat mixed with cement). The research work began with identifying sampling location, and continued with various types of field and laboratory tests. Each required test has been conducted based on its specified standard. A summarized flow chart shown in Figure 3.1 presents the designed program throughout the research.
3.2
Sampling location
Preliminary studies were conducted to choose the most suitable place for sampling. Several places located in Malaysia such as Bukit Changgang, Klang, Kampung Sri Nadi, Klang, and Kamung Jawa, Klang for this purpose were studied. The most influencing factors considered were, availability of suitable type of peat, easier access to the sampling site, and travelling time to the site.
At the final stage of sampling site determination, it was decided to use peat samples obtained from Kampung Jawa, Klang (Selangor), in the western part of Malaysia for the entire research project. Figure 3.2 shows the geographic location of the sampling.
Figure 3.1: Flow chart for the study 60
3.3
Soil sampling
For the research project, there were two types of soil samples collected: undisturbed and disturbed. Collections of samples were based on the instructions described by BS (1377). Samples were collected from test pits or bore holes at various depths from 50 mm to 1000 mm from the surface ground level. Undisturbed samples were taken using hollow circular thin walled diameter samplers, that were pushed in to the ground as is shown on Figure 3.3 (a), as well as using UPM sampler shown on Figure 3.3 (b). After the samplers were filled with peat samples, each sampler was vertically pulled out from the ground. Undisturbed samplers used had area ratio (AR) of below 10%, (equation 2.6), and also inside clearance ratio (ICR) of close to 1% (equation 2.7).The undisturbed samples (Figure 3.3c) while in their original samplers were sealed to prevent any moisture loss. The collected undisturbed samples then carefully transferred to the soil laboratory without any disturbances for performing different types of tests such as CBR, UCS, triaxial test, Rowe cell and permeability tests. The disturbed samples (Figure 3.3d) were also collected and were placed in plastic bags and were taken to soil laboratory for cement treated peat’s CBR, UCS, compaction, classification, and index property tests.
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Sampling lo c a t io n
Figure 3.2: Distribution of peat land in Malaysia, and sampling location for the research
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a)
b)
c)
d)
Figure 3.3: Sampling collection procedures (a, b, and c) for undisturbed samples, and (d) for disturbed bulk samples 3.4
Index property determination tests
Some of the most useful parameters to identify, and describe peat were assessed and measured in the research either at field or in the laboratory includes:
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3.4.1
Field identification tests
Using test pits, at the field, the 10 degrees of humification (H1 to H10) in the von Post (1922) classification system (Appendix D, Table D1), which are determined based on the appearance of soil water extruded when the soil is squeezed in the hand, were examined. Also the Ground water table (GWT) conditions were measured during raining and hot days. GWT was measured from the surface of ground level. Figure 3.4 depicts a test pit for soil identification strata as well as GWT measurement at the field.
Figure 3.4: A test pit to check for soil’s strata and depth of ground water table 3.4.2
Moisture content (ASTM D 2216)
Small and representative amount of untreated (plain) or treated peat (peat mixed with cement) samples were weighed as received, and then oven dried at 105°C for 24 hours. The sample was then reweighed, and the difference in weight was assumed to be the weight of the water driven off during drying.
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3.4.3
Consistency limits (BS 1377, and ASTM D 424)
Representative dried samples both for plain peat, or treated peat (peat mixed with cement, and additives) were subjected to liquid limit (Figure 3.5), and plastic limit tests. The plastic limit was detected by considering the lowest moisture content at which the samples could be rolled into a 3.2 mm (1/8") diameter thread without breaking. Also, for each soil based on the liquid limit, and plastic limit values, plastic index (PI) was obtained. Consistency limit tests have been conducted on various samples during their fresh mixings from just after mixing and up to 30 min after.
Figure 3.5: Liquid limit (cone penetration) test 3.4.4
Organic contents (ASTM D 2974)
The organic content of each peat sample was determined by first oven-drying a representative sample of each soil at 105°C for 24 hrs, then recording the moisture content. The sample was then placed in a muffle furnace (Figure 3.6) heated to 450°C for 5 hrs then reweighed after nearly constant mass was achieved. The ash content of the samples was then recorded as the weight loss due to ignition divided by the initial dry weight. The organic content was then calculated using Equation 2.1. 65
Figure 3.6: Organic content samples in the furnance 3.4.5
Grain size distribution (ASTM D 421)
Before conducting the sieve analysis for the peat sample, using mechanical method, a representative of the soil was dried gradually to a constant weight in the oven with temperature around 50°C. Gradual drying of peat was used to prevent lumps in the sample, and also to keep the natural texture of the peat as much as possible. Peat grain size was then determined by sieving a quantity representative dried sample, which was reduced from the lumps in the sample to elemental particle size through a stack of sieves of progressively smaller mesh opening from top to bottom of the stack (Figure 3.7). The quantity of samples retained on a given sieve in the stack is termed one of the grain sizes of the peat sample. Percent passing for each sieve in the stack was computed, and used to plot a curve of percent passing versus grain diameter.
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Figure 3.7: prepared peat sample for sieve analysis test 3.4.6
Specific gravity (ASTM D 854)
Values for specific gravity of sample solids were determined by placing a known weight of oven-dried sample in a flask with water. The weight of displaced water was then calculated by comparing the weight of the sample and water in the flask with the weight flask containing only water. The specific gravity was then calculated by dividing the weight of the dry sample by the weight of the displaced water. Figure 3.8 shows saturated peat samples in distilled water while being vacuumed inside the desiccator.
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Figure 3.8: Saturated peat samples in desiccator for specific gravity test 3.4.7
Fibre content (ASTM D 1997)
Fibre content was determined for the plain peat samples from dry weight of fibres retained while washed on sieve # 100 (> 0.15 mm opening size) as percentage of oven dried mass.
3.4.8
Linear shrinkage (BS 1377)
Representative samples were passed through sieve 425 μm and wetted with moistures close to their liquid limits. Then, either plain peat or treated peat (peat mixed with cement) samples were placed in the standard bar [Figure 3.9 (a)], and left in the oven to be dried [Figure 3.9 (b)]. The linear shrinkage was measured as a percentage of the original length of the specimen.
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a)
b)
Figure 3.9: Linear shrinkage test samples a) Before drying, and b) After being dried 3.4.9
pH (ASTM D 4972)
The pH values of each untreated (plain) as well as treated peat (peat mixed with cement) soil samples were conducted by first air drying the samples and then subjecting them to 100 percent saturation using distilled water. Values of pH were then measured using a calibrated pH probe (Figure 3.10). The test conducted on both control (untreated) and all the treated peat samples.
Figure 3.10: Digital calibrated pH probes
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3.4.10
Moisture – unit weight relation (compaction) [ASTM D 1557]
Modified compaction tests have been used to find maximum dried unit weight or γd(max), and optimum moisture contents (OMC) or wopt for the plain peat, as well as treated peat samples with ordinary Portland cement (OPC).
Prior to the laboratory compaction tests, due to high moisture contents of the wet peat samples with water content of over 185% (natural water content of peat samples), the moisture content of the peat samples were reduced to around 50%. Reducing natural moisture content of the peat samples was first done by leaving the peat samples in the oven with low temperature of below 60˚C for 4 to 8 days. In order to release the confined moisture inside the peat samples, every day the samples were taken out of the oven and mixed, and again were placed back inside the oven.
This gradual drying of peat samples procedure has been used instead of usual method of complete drying of peat to prevent the possible change of peat samples texture upon complete drying inside oven. Figure 3.11 shows moisture content reduction process for the bulk peat samples as well as the reduced moisture content of peat samples prior to be used for compaction tests.
Also, compaction tests have been conducted on various types of ordinary Portland cement (OPC) and treated fibrous peat samples with or without additives. Prior to these compaction tests, the specified amount of peat, OPC with or without additives mixed in an electric dough mixer to achieve uniformity for at least ten minutes. The compaction process was also done with the help of an electric compacting machine, and this insured more uniform compaction for all different mixtures that compaction tests were conducted on them.
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a)
b)
Figure 3.11: Moisture content reduction process of field fibrous peat (a) Gradual moisture content reduction or half drying of peat procedure in the oven, and (b) Reduced moisture content samples to be used for compaction tests From each set of compaction tests, moisture-density curve has been constructed and from its result the optimum moisture content (wopt) and maximum dry unit weight (γd(max)) were detected. Number of points used to construct the compaction curves throughout the experimental compaction work has been from 3 to 8 points. The results of compaction tests were used for UCS, and CBR tests as well as constructing precast stabilized fibrous peat columns, which are going to be explained in details later in this chapter. 3.5
Mechanical properties determination tests
Mechanical properties of peat are represented by some important parameters that show their response or reactions either when they are subjected to water intrusions, and their hydraulic conductivities or when they are subjected to an external load. Some of these parameters that were studied in this study are presented in the next following sections.
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3.5.1
Permeability (ASTM D 2434)
One of the reasons to measure permeability of soil is to evaluate its hydraulic conductivity, and also investigate the quantification of water during pumping for underground construction. In order to find coefficient of permeability for the peat ground at the field, undisturbed peat sample was subjected to laboratory falling head permeability tests.
3.5.2
Unconfined compressive strength or UCS (ASTM D 2166)
Unconfined compressive strength tests were conducted on the undisturbed fibrous peat samples (Figure 3.12a) and treated peat (peat mixed with OPC with and without additives) samples as one of the strength evaluation tests. Generally, the size of the samples was 38 mm in diameter and 76 mm long [Length (L)/ Diameter (D) = 2]. This test was conducted to measure the unconfined compressive strength values (qu) of various types of samples. For those samples that had a different L/D ratio than equal to 2, a correction factor according to Table 2.7 was used to calculate qu.
The prepared mixtures were placed in three layers in a UCS splitable brass mould to make reconstructed treated samples having an internal diameter of 38 mm and L/D ratio of 2. Each layer was given 10 constant full thumb pressures of approximately 10 seconds for compacting the samples as is a common practice in Sweden (Axelsson et al. 2002), then trimmed at both ends (Figure 3.12b).
Due to the longer size of steel fibres when used as additives to OPC treated fibrous peat samples, the 101.2 mm (4") standard compaction moulds was used to mould the samples. Each sample was compacted in three layers then, and each layer was given 25 blows by 2.2 kg (5 lb) rammer (proctor compaction test). Treated unconfined compressive strength samples with OPC were tested either under unsoaked (Figure 3.12c) or soaked (Figure 3.12d) conditions. 72
The term unsoaked, in this study is used for those samples that were tested at the end of their curing periods, without being submerged in water, while soaked samples were first completed their curing period under their curing condition, and then prior to be tested were submerged (soaked) in water for a few days to become completely saturated. Throughout this study, some types of identical OPC treated fibrous peat samples were tested for their strength under both unsoaked as well as soaked conditions. At least two specimens used to estimate UCS values of each type of samples, and the average UCS value of the two obtained was recorded as q u for that particular sample in this study. a)
b)
c)
d)
Figure 3.12: Unconfined compressive strength samples, a) Undisturbed sample, b) Reconstructed treated peat (peat mixed with OPC) sample, c) Unsoaked samples, d) Soaked samples
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3.5.3
California bearing ratio (CBR ) [(ASTM D 1883)]
In this study, in order to evaluate the strength of various types of peat samples, CBR tests have been carried out on both, undisturbed fibrous peat as well as treated fibrous peat (stabilized) samples. CBR tests on OPC treated fibrous peat samples were conducted on the well mixed samples made of specified amount of fibrous peat, ordinary Portland cement, and various types of additives. They were mixed in electrical dough mixer for at least 10 min before being placed in standard CBR moulds. Also, each sample was placed in 152.4 mm (6″) mould by 5 layers, and each layer was given 56 uniformly distributed blows of 4.54 kg using electrical compacting machine.
The undisturbed peat sample for CBR test was obtained in a thin walled mould of 152.4 mm (6″) in diameter that is the standard size for CBR moulds. Sampling was done based on undisturbed sampling procedures described in section 3.3 and is shown on Figure 3.3a.
CBR value for each sample undergoing CBR test either in undisturbed or stabilized status was calculated based on the procedure described in section 2.7.8. Also, CBR values reported in this study for various types of samples were based on three penetration ratios of 2.5 mm (0.1″), 5 mm (0.2″), and 7.5 mm (0.3″). Among the three penetration ratios obtain in any CBR tests, the highest value of them was chosen and reported as the CBR value for each tested CBR sample.
CBR strength evaluation tests have been conducted on two different types of samples: unsoaked, and soaked (saturated in water). Figure 3.13 shows treated fibrous peat CBR samples at their unsoaked and soaked conditions.
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a)
b)
Figure 3.13: Treated CBR peat samples at their a) air curing, and b) air cured and then soaked conditions, before being tested for their CBR strength values 3.5.4
Consolidation undrained (CU) triaxial (ASTM D 4767)
Consolidated undrained triaxial tests have been conducted to evaluate the shear strength of undisturbed fibrous peat, as well as undisturbed fibrous peat samples reinforced with various types of precast stabilized peat columns. All the peat samples used in triaxial tests were undisturbed and had a diameter of 50 mm, with L/D ratio of 2.
All consolidated undrained test samples were conducted by computerized program using GDSLAB v 2.2.7 (Figure 3.14). Each sample was first saturated in five stages by 10, 20, 30, 40, and 50 kPa until Skempton B-value was detected, and then automatically was consolidated up to 100% using 50 kPa pressures. At the final stage each sample was sheared to failure while confined with the specified confining pressures.
For all samples, the consolidation pressure of 50 kPa was used. Confining pressures used to fail each set of samples were; 50, 100, and 150 kPa respectively. The strain rate of 0.24% per minute was used to shear the samples. The numbers of samples for each set of tests used in each experiment varied from 75
two to four, with some tests had to be repeated. The total time length for each single sample to be tested was at least 24 hrs.
Figure 3.14: Computerized consolidated undrained triaxial test in progress 3.5.5
Rowe cell consolidation (ASTM D 2435, BS 1377)
According to Lee et al. (1983), the Rowe cell consolidation apparatus was first introduced by Rowe and Barden in 1966 to overcome the disadvantages of the conventional oedometer test when performing consolidation tests on non-uniform deposits such as fibrous peat. Rowe cell has several advantages over the conventional oedometer test apparatus. The main features responsible for these improvements are the hydraulic loading system, the control facilities, the ability to measure pore water pressure and the capability of testing samples of a large diameter. Figure 3.15 shows details of the Rowe cell consolidation apparatus, and process used in the study.
In this research, Rowe cell tests were used to investigate two parameters that are most effective in compressibility behaviour of saturated soft soil, namely: modified compression index (Ccε) and recompression ratio (Crε). Rowe cell tests were conducted on undisturbed peat, as well as undisturbed peat samples reinforced with various types of prepared precast columns. 76
All the peat samples used in Rowe cell testing were undisturbed fibrous peat, and prior to be tested all have been 100% saturated (Figure 3.16). Also all the samples had a diameter and a height of 150, and 50 mm (equal to inside dimensions of the Row cell) respectively. All loading and un-loading procedures were done by computerized program using GDSLAB v 2.2.7. For all samples, the load increment ratio used was one (LIR = 1), and each loading or unloading process was continued for 24 hrs. The loading procedure started from 20 kPa, and continued through 320 kPa. After five days of loading (for 20, 40, 80,160, and 320 kPa) each sample was unloaded from 320 kPa to 40 kPa. Throughout the experimental procedures, the samples were single drained from the bottom part of the Rowe cell as is shown in Figure 3.15a. Three sets of data were recorded by the computer every 15 seconds. The data recorded were; time, deformation, and pore pressure. a)
b)
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c)
d)
Figure 3.15: Details of Rowe cell consolidation test: a) Schematic diagram of Rowe Consolidation cell (Lee et al. 1983) b) Rowe Cell consolidation test set-up (Duraisamy et al. 2007) c) Computerized Rowe cell consolidation in progress d) A sample after complete consolidation process inside the disassembled Rowe cell
Figure 3.16: A saturated sample inside the prepared steel mould during saturation period, and, prior to be placed in Rowe cell for consolidation 3.6
Static load bearing capacity test
The selection of allowable pressure is one of the major concerns in the foundation design process. Field load bearing capacity tests can be considered the most reliable sources to evaluate the foundation design parameters. Tests such as plate load tests, or pile load tests are usually conducted at the fields to 78
estimate the load bearing capacity of the respective ground, or to confirm the design assumption. Kaniraj (1988) describes pile load test as the acid test for the actual performance of piles at the site, and its purpose is to determine the ultimate load capacity of pile.
According to ASTM, there are several types of field tests that can be used to estimate load bearing capacity of the ground. Some of these tests include: plate bearing test (ASTM D 1194), repetitive static plate load tests of soils (ASTM D 1195), and non-repetitive static plate load tests of soils (ASTM D 1196).
In this study, bearing capacity of fibrous peat has been investigated through static load bearing capacity test. The test has been conducted not at the field rather was reconstructed in a designed and fabricated large circular mild steel test tank (Figure 3.17) that resembled the field condition. For carrying out the plate load test, the tank was filled with remoulded natural field fibrous peat up to a depth of 1.0 m, so the bulk unit weight of remoulded peat inside the test tank was equal to the field bulk unit weight (10.04 Mg/m3). Test tank had an 820 mm diameter and a total of 1600 mm in height. The wooden plate used to transfer the imposed load uniformly over the soil had 60 mm thickness, and 600 mm diameter.
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Figure 3.17: Schematic diagram of the test tank Load bearing capacity tests were carried out on reconstructed (remoulded) fibrous plain peat and also remoulded fibrous plain peat reinforced with various types of precast stabilized peat columns. The load bearing tests procedures as well as the instruments used during each test are shown in Figure 3.18.
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Figure 3.18: Schematic loading diagram procedure during load bearing capacity tests To prevent the leakage of water from the test tank, plastic sheet was used to line the tank and at the same time it was useful in reducing the friction between peat and the wall of the test tank during each test. The testing procedure used in the experiment was very similar to the testing procedure for plate bearing tests specified by ASTM D 1194. This was done by applying load to the plate in steps of 1 to 4 kN each, by means of manual pumping and hydraulic jack, and up to a time when the rate of settlement showed significant reduction to a value of 0.02 mm/min. Then, the next increment of 1 to 4 kN was applied, and the observation repeated. The test was continued until significant settlement of over 600 mm (10% of the plate load diameter) and up to 800 mm was detected or a complete failure of the soil underneath the plate was occurred. Also, after completion of loading procedure for some selected tests unloading procedure was conducted in similar but reverse and backward steps of loading process.
81
Measurements throughout each test were recorded by means of display unit, TM logger, and also use of WINCLISP v4.48 computer software program. Quantitative load bearing capacity of the fibrous peat at various conditions was estimated based on a graph that was plotted with the mean deformations versus bearing pressures.
3.7
Field vane shear test (FVST)
The field vane shear test is the most commonly used method for measuring the undrained shear strength of soft to stiff clays. Researchers also use this test to measure the shear strength of peat deposits as well. Application of this test in the field for preliminary investigation of soft soils is fully relevant as well as economic. Hand held vane tester has also a good repeatability and is quick in providing valuable information for the planning of more detailed surveys.
This test was conducted at the field up to 3 m depth from the ground level. The apparatus used for this purpose was the original Genover H-60, hand held vane tester, that would provide the shear strength from direct reading on its handle (Figure 3.19). In this study, FVST has been used for preliminary evaluation of undrained field shear strength of peat (Figure 3.20).
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Figure 3.19: Geonor H-60, hand-held field shear vane tester (units in mm) [Geonor 1995]
Figure 3.20: Hand –held field vane tester is being used to measure the undrained shear strength of peat at various depths
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3.8
Shallow (mass) stabilization of fibrous peat
In general, shallow stabilization of peat ground refers to strengthening of the top layer of peat ground that can serve as a reliable subgrade for road constructions. The shallow depth for this purpose may be considered from 200 to 250 mm (8 to 10 inches) from the ground level. Laboratory research was conducted to evaluate the strength of stabilized fibrous peat with ordinary Portland cement, with and without five types of additives. As discussed in chapter two with details, additives used in this study were; polypropylene fibres, silica fume, steel fibres, ground granulated blast furnace slag, and fly ash that were mixed in different dosage amounts with ordinary Portland cement to stabilize peat. Strength evaluations conducted for each types of stabilized sample were; UCS, and CBR.
3.8.1
Mixtures preparation for strength evaluation tests
Prior to mould or reconstruct the mixtures of OPC treated fibrous peat samples in to UCS or CBR moulds, each stabilized peat mixture was prepared according to specified dosage amounts of OPC, and additives. Two types of mixtures were prepared, and moulded; first mixtures were prepared with fibrous peat’s soil at its natural moisture content, and the second type of samples were prepared based on each mixture optimum moisture content’s value obtained from moisture-density curves.
3.8.1.1
Mixture preparation using natural moisture content of peat
In this type of mixing, the peat at its natural moisture content (wet) was screened in order to remove the larger size of vegetal fibres using a 6.3 mm (0.3˝) sieve, and then specified amount of OPC, as well as various types of additives were added to the screened fibrous peat and mixed well for homogeneity, using malt mixer for five minutes (den Haan 2000).The prepared mixture was then placed in UCS moulds as it is described in section 3.5.2. 84
Also, larger quantities of mixtures were used, if the prepared mixtures were to be used for CBR tests. For mixing larger quantity of CBR samples, electrical dough mixer was used for at least 10 min before placing stabilized mixtures in standard CBR moulds, as it is described in section 3.5.3.
3.8.1.2
Mixture Preparation using optimum moisture content values of various samples
types of
This type of test was conducted for CBR evaluations. Due to the initial high moisture contents of the original peat samples, gradual drying of natural peat samples procedure that is already been explained in section 3.4.10 has been used instead of usual method of complete drying of peat to prevent the possible change of peat texture upon complete drying inside oven.Then specified amount of ordinary Portland cement as well as additives, and water were mixed to bring each mixture to its OMC condition. In the final stage of sample preparations, each mixture was moulded in standard CBR mould according to the described procedures in section 3.5.3. 3.8.1.3
Ordinary Portland cement, and additives dosage rates
Ordinary Portland cement (OPC) and five types of additives: polypropylene fibres (PPF), silica fume (SFU), steel fibres (StF), blast furnace slag (BFS), and fly ash (FA) have been used to treat peat samples. Various amount of ordinary Portland cement from 5 to 50% ordinary Portland cement was used in different cement treated peat samples. Amounts of OPC used in the study were based on the total wet weight of the peat at the time of the mixing. For example, 5% OPC means 5 g of OPC in dry form has been added to 100 g of the wet peat (weight of dry peat + weight of water in the peat), and also 50% OPC means 50 g of ordinary Portland cement powder has been added for each 100 g of wet soil.
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Due to variations in; natural unit weights (10.2 – 10.4 kN), moisture contents (200 – 400%), and also nonuniformity of fibrous peat (H1-H4), it was decided to use cement weights per total weight of each freshly used peat samples [at peat’s natural or instant’s moisture content] every time that the mixtures of OPC treated peat samples were prepared during the entire research process.
Dosage amount for four types of additives out of five namely; blast furnace slag, fly ash, polypropylene and steel fibres were also based on the total wet weight of peat at the time of mixing. For example 0.15% of polypropylene fibres means 0.15 g polypropylene fibres was added to each 100 g of wet peat, or 15% blast furnace slag (or fly ash) means 15 g blast furnace slag (or fly ash) was added to 100 g of wet peat, and in similar manner 2% of steel fibres, means 2 g of steel fibres was added to each 100 g of wet peat.
For silica fume as the fifth additive, dosage amounts in the OPC treated peat samples were based on the weight of the ordinary Portland cement used in the mixtures. For example 5% silica fume means in each 100 g of ordinary Portland cement used in the mixture, 5 g of silica fume was added.
3.8.1.4
Optimum dosage rates for additives
For each type of additives to be used in this study, the most effective amount or optimum dosage rate was determined based on trial and error procedures. In this method, different dosage rates of additives were used to make OPC treated samples. According to this procedure the trial which provided with the highest strength result was chosen as the optimum or most effective dosage rate of that particular additive. The strength evaluation tests used for this purpose were UCS, and/or CBR. For four out of five additives used in this research namely; polypropylene fibres, silica fume, blast furnace slag, and fly ash trial and error method used to find the optimum dosage rate of each, and for the fifth additive or steel fibres trial and error method was not used, and instead only two dosage rates of 2%, and 4% 86
which were considered low dosages that are commonly used in concrete (mixture of coarse grain mineral soils and cement) were used. Trial and error procedure was used on samples prepared from different dosage rates of each additive, inclusive OPC and fibrous peat at peat’s field or natural moisture content.
3.8.2
Types of curing techniques
As discussed earlier in chapter two, the most usual methods among engineers so far to deal with peat deposits have been either to remove the peat and replace it with suitable soil or to pass piles through it to the stronger soil layers below. On the other hand, researches have been carried out to discover ways to strengthen peat deposits. These methods include; peat stabilisation using a mixture of various binders such as cement or lime, and different admixtures such as fly ash and blast furnace slag (Hampton and Edil 1998; Axelsson et al. 2002; Hernández and Al-Tabbaa 2004; Hayashi and Nishimoto 2005).
The cementation and pozzolanic reactions have been investigated in detail by Bergado et al. (1996), Janz and Johansson (2002), Hwan Lee and Lee (2002) as well as Tremblay et al. (2002). Since, the peat already has a high water content, required water for soil-cement reaction comes from it. Therefore, dry jet mixing (DJM) method is effective for peat stabilization instead of wet mixing method (Yang et al. 1998). This method is classified as dry-rotary-end. That means introducing dry binder pneumatically, rotary method for the penetration of soil and mixing the soil with the binder and end for location where the mixing is conducted (Bruce et al. 1999). This method seems to work well for soft silty clay though its application for peat is yet to be proven. Hence, this model study was initiated in order to evaluate the effectiveness of dry mixing method in peat.
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The effects of three curing techniques on the unconfined compressive strength of stabilized fibrous peat with OPC have been evaluated with different curing periods of just after mixing as control measure samples as well as 28, 90, and 180 days. The curing techniques used in the study were; air curing, moist curing and moist curing with surcharge load of 10 kPa. The second and the third are the traditional methods, and have long been used to cure stabilized peat samples with OPC, but the first one seems to be in a nascent stage as very few literatures are available. In the following sections these three curing techniques are discussed with more details.
3.8.2.1
Air curing
The air curing can be defined as a process of mixing peat with cement and exposing this mixture to air for curing, without any water to go in to the mixture during curing period. This air curing technique was adopted as the natural water content of the fibrous peat was very high (187 - 417%). OPC was added to fibrous peat at its natural water content as it was believed that this moisture content (samples prepared at this moisture content) will be enough for the complete reaction with cement to take place and at the same time it also represents the in-situ condition.
The samples were prepared in mould, taken out after compaction and then wrapped in thin plastic sheet and kept in air at a room temperature of 30 ± 2 °C, and humidity of 80 ± 5% during the curing period, as shown in Figure 3.21. Also, the top portion of the samples was kept open and exposed to air to allow the movement of moisture from the top only and not from the sides to represent closely the in-situ condition. The procedure can be simulated at field by keeping the ground water table lowered during the curing periods by pumping.
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Figure 3.21: UCS samples in air curing condition
3.8.2.2
Moist curing
In moist curing, the samples were prepared in mould as explained above and were taken out from the mould and kept submerged in water during curing periods, as is shown in Figure 3.22. The procedure resembles the normal field condition, after stabilization.
Figure 3.22: UCS samples in moist curing condition
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3.8.2.3
Moist curing with surcharge load
For moist curing with surcharge load, samples were subjected to 10 kPa during the curing periods. The procedure used for this curing technique is explained through the following explanation as well as the Figures. The procedure may be resembled at normal field condition while the stabilized peat is submerged in water, and is being loaded either by its own upper weight (overburden pressure) or by extra surcharge load during curing period.
Non-reusable plastic tube moulds made of hard plastic sheets, and transparent tape, with their surface perimeter vertically cut, as shown in Figure 3.23a, were prepared. The purpose of the vertical cuts on the side of the moulds was to permit the full water penetration of the samples during the curing period. The next step was to place the stabilized peat samples in the moulds according to procedure described in section 3.5.2, and then the stabilized samples were completely submerged in water while at their racks, as shown in Figure 3.23b.
Cement mortars (sand, cement, and water) cylinders with diameter of 37mm (1 mm less than the diameter of the stabilized peat samples, and identical lengths), that were prepared earlier and are shown in Figure 3.23b, were placed on top of the stabilized peat samples in order to transfer the surcharge load to each sample, as shown in Figure 3.23c. Finally, the steel surcharge load, by means of a plate, was placed on the top of the cement mortar cylinders during the curing periods, as shown in Figure 3.23d. For example, the total surcharge load used for four samples shown in Figure 3.23d was 40 kPa and therefore 10 kPa for each sample during the curing periods.
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a)
b)
Vertical cuts
Stabilized submerged samples
Mortar cylinders Surcharge load Plate
c)
d)
Figure 3.23: Moist curing plus 10 kPa surcharge load procedure: a) plastic tube moulds, b) moulded samples are submerged in water, mortar cylinders, steel weight, and plate are also shown, c) concrete cylinders are placed over the submerged samples, d) the steel weight is placed on top of the concrete cylinders on a plate to exert a total of 10 kPa load on each sample
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3.8.3
Linear volume shrinkage index (LVSI)
Due to chemical reactions and dehydrations, the stabilized fibrous peat samples in this study showed linear shrinkages in diameters as well as in lengths from their original diameter and length sizes when subjected to air curing procedures. Also, as the curing periods became longer more shrinkage was detected.
Since air curing of the OPC treated peat is in nascent stages, and shrinkage of the treated peat samples occur as the curing periods begins, and continues through the curing periods, it was necessary to find a suitable, and proper test to measure this phenomena for the various types of air cured stabilized peat samples that contained different amount of ordinary Portland cement and additives. Thus, the test was given a title or name “linear volume shrinkage index” or “LVSI”, and main procedure to determine its value include; a) Mixtures of stabilized peat samples were compacted at their OMC and to their maximum dried unit weights (found from compaction tests) inside the standard CBR moulds according to ASTM D 1557. b) The moulded stabilized peat samples were left inside an oven with a temperature of 70 ± 2˚C for 120 hours (five days) for a complete gradual drying process of reaching to constant dried weights. c) After five days of the above-mentioned complete gradual drying of the samples, the shrunken diameters as well as lengths of the samples were measured to the nearest 0.01 mm. d) The LVSI of the stabilized peat samples was then calculated using the following relation (Equation 3.1), and expressed in per cent (%). LVSI (%) = 100 - (Volume after shrinkage / Original volume) × 100
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Eq. (3.1)
Because of shrinkage phenomena, air cured stabilized CBR samples were shrunken during curing periods and slipped out of their standard moulds at the time of CBR tests, as is shown in Figure 3.24. Therefore, flexible sized moulds made of double thick plastic sheets and steel clamps were prepared for them, during the actual CBR test procedure as shown in Figure 3.25.
Figure 3.24: 90 days, air cured shrunken stabilized CBR samples after easily removal from their standard sized moulds, and prior to be securely placed in flexible CBR mould for CBR test
Figure 3.25: A shrunken stabilized sample is wrapped and clamped securely in the prepared flexible mould prior to being tested for CBR 93
3.9
Test to determine time for saturation by soaking in water
To resemble samples according to the field condition, it was required to measure the strength values of the soaked samples along with the unsoaked samples. In order to determine the shortest time that any stabilized sample can be completely saturated, those types of stabilized samples that provided the highest strength values among all other types of mixture used in the study were chosen to be soaked. And their soaking periods to reach complete saturation (100%) were used for all other stabilized samples as well. This was done, because it was assumed that samples with less strength values saturate in less time than those samples with higher strength.
Chosen mixtures were placed in CBR moulds at their OMC, and compacted to their maximum dried unit weights found from compaction tests described earlier in section 3.4.10. According to, ASTM D 1883 minimum soaking period of CBR samples for normal (mineral) soils is 96 hours or four days, but there was not a required procedures to soak the cement treated peat samples available. Therefore a soaking method for this study needed to be developed. The main concern was, when or after how many days a soaked OPC treated fibrous peat sample would become 100% saturated.
Saturation degree of soils is usually is detected with the aid of electric moisture meter or elcometer, which measures the amount of moisture in the soil by measuring the resistance to electric current. Water is a greater conductor of electricity, so the more water in the soil, the less resistance is indicated.
In this study, chosen CBR samples were submerged in water, and their weights were checked and recoded for every 24 hrs. Weight increase of the samples due to water absorption, and thus increasing in saturation degree were continued until there were no increases in their weights, and successive 94
weights results showed constant values. The earliest time period that a soaked OPC treated peat sample reached its constant saturated weight was considered as the complete or 100% saturation period of the sample.
3.10
Deep stabilization of fibrous peat
In this research, an attempt has been made towards deep stabilization of tropical fibrous peat in laboratory using a new technique. This technique uses precast columns made of peat, OPC, with or without additional amount of additives to reinforce fibrous peat deposit. Precast stabilized peat columns have been evaluated for their shear strength and resistant to deformations when reinforcing undisturbed fibrous peat samples. Strength evaluation of reinforced fibrous peat with various types of precast stabilized peat columns were studied through consolidated undrained triaxial tests. Also modified compression indices, and recompression ratios of the reinforced fibrous peat with various types of precast columns have been investigated through Rowe cell consolidation tests. Types of additives used in precast OPC treated peat columns were; polypropylene fibres (PPF), silica fume (SFU), ground granulated blast furnace slag (BFS), and fly ash (FA).
Also, load bearing capacity of precast stabilized fibrous peat columns have been evaluated by means of a large test tank, reconstructed with fibrous peat, and reinforced with various types of precast stabilized fibrous peat columns made of OPC, and additives. Types of additive used for OPC treated fibrous peat columns to reinforce the remoulded fibrous peat inside the test tank were; polypropylene fibres, silica fume, and a mixture of polypropylene and steel fibres.
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3.10.1
Preparation of precast stabilized peat columns, and samples for CU tests
The process of making precast stabilized fibrous peat columns included mixing fibrous peat with a specified amount of ordinary Portland cement, (with or without optimum dosage of additives) at their optimum moisture (found from compaction tests) contents. The mixture was then compacted into moulds and left to dry. As the stabilized columns dried out, they gained strength due to dehydration, and chemical reactions. When drying was completed, they were taken out of their moulds and inserted in the pre-drilled holes.
For each type of precast stabilized peat columns a set of three identical samples were prepared, and each sample was tested in triaxial machine as described in section 3.5.4. Cement treated columns made of specified amounts of fibrous peat, ordinary Portland cement, with or without additives, had their respective optimum moisture content, found from moisture - density curves as described in section 3.4.10. Column dimensions consisted of 16.67 mm diameter, and 100 mm length. The area ratio of the columns with respect to samples used for triaxial tests (area of the column/ area of the peat sample) was 0.11 and, even the columns are considered of less structural members compared with piles, their dimensions in this research have been tried to be in accordance with the most commonly used pile spacing specified by several building codes described by Bowles (1983). The code suggests the optimal spacing (centre to centre distance of columns) is in the order of 2.5 to 3.5 D (D is the diameter of the pile or column) and in this research the column spacing was 3.0 (50/16.67). Also length divided by the diameter ratio of the columns in this research was 6 (100/16.67).
After the mixture of stabilized peat had been prepared, the mixture was placed in non-reusable moulds made of plastic sheet cover and tapes in a form of plastic tubes (Figure 3.26a). Each mixture of peat was placed in five layers, and each layer of stabilized mixture was given 56 blows with a metal rod 96
weighing 384 grams while inside its mould (Figure 3.26b). Then the prepared samples with their moulds were subjected to the drying process. In order to prevent possible cracking in the prepared samples owing to the high temperature of drying, the prepared column samples were placed inside an oven with a temperature of 70 ± 2˚C. By this gradual drying process, within three days, they reached to a constant dried weight. Then the dried samples were taken out of their moulds (Figure 3.26c). a)
b)
c)
Figure 3.26: Moulding precast columns: a) Non-reusable moulds (plastic tubes) made for columns, b) Compacting a layer of mixture in the mould, c) Dried columns out of their moulds Undisturbed peat samples were placed inside the standard steel mould of triaxial tests with each sample with length and diameter dimensions of 100 mm and 50 mm respectively covered with rubber 97
membrane. Using a laboratory prepared thin wall (0.25 mm) metal tube cutter of the same size as the column diameter (Figure 3.27a) a hole was made at the centre of the undisturbed peat sample (Figure 3.27b). The precast stabilized peat column was then inserted in to the hole as depicted in Figure 3.27c. Finally, undisturbed peat samples along with the columns at their centre were placed in the triaxial cell for actual consolidated undrained tests as described in section 3.5.4.
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a)
b)
c)
Figure 3.27: Installation of precast columns: a) Thin-walled metal tube cutters used to make hole at the centre of undisturbed peat samples, b) Precast stabilized peat column to be inserted in the centre of triaxial undisturbed peat sample, c) Triaxial undisturbed sample with the precast stabilized peat column placed at its centre 3.10.2
Preparation of precast stabilized peat columns, and samples for Rowe cell consolidation tests
The precast columns, made of specified amounts of peat, OPC, with or without optimum dosage amount of additives, were prepared by compacting them at their respective optimum moisture contents found from moisture – dry unit weight curves. The columns were 50 mm in diameter and 50 mm long
99
and had an area ratio of the 0.11. As was discussed in previous section (3.10.1), the code suggests the optimal spacing between the columns to be in the order of 2.5 to 3.5 D (D is the diameter of the column) and in this study the column spacing was considered to be 3.0 (150/50).
Non-reusable plastic casings made of thick plastic sheet and transparent tapes (Figure 3.28) were used to mould the stabilized peat samples (Figure 3.28).
Figure 3.28: Precast peat columns and non-reusable plastic moulds Each prepared mixture of peat, various amount of OPC with and without additives were transferred into the prepared moulds in five layers and each layer was compacted by giving 56 blows with a hammer weighting 384 g. The prepared samples together with their moulds were then kept in oven for four days to reach a constant dried weight. The temperature used for this purpose was 70 ± 2°C. Figure 3.29 depicts the procedure used to prepare a final sample with a precast column at its centre. After the sample was prepared as shown in Figure 3.29, it was submerged in water to be completely saturated (Figure 3.16). After seven days of saturation period, the sample was placed inside the Rowe cell for actual consolidation test. The procedure followed for preparing the samples and conducting the tests were same for all the samples either untreated fibrous peat or fibrous peat treated with stabilized columns samples as described earlier. 100
a)
b)
c)
d)
Figure 3.29: Columns installation procedure: a) Undisturbed peat sample, b) Thin walled metal tube cutters inserted in the undisturbed peat sample, c) Sample with hole prepared for the column, d) Stabilized peat column inserted in the undisturbed fibrous peat sample 3.11
Preparation of precast columns for load bearing capacity tests
The general procedure adopted to prepare the columns was identical to the procedure of making columns during triaxial, or Rowe cell tests. Precast stabilized fibrous peat columns used for load bearing capacity tests were in larger scales than those used in triaxial or Rowe cell tests. In this test, load bearing capacity tests were conducted on remoulded (reconstructed) plain fibrous peat as well as six different types of precast columns while being installed at the centre of remoulded fibrous peat inside the test tank. Five columns had diameter of 200 mm, and one column was tested with 300 mm diameter. Each column was made of OPC, with and without different additives. The additives in this 101
type of tests used to make columns were silica fume, polypropylene fibres, and also a combination of polypropylene and steel fibres. The length of all columns used in load bearing capacity tests were 1000 mm (L/D = 5, and L/D = 3.3).
Each mixture of stabilized fibrous peat for use in precast columns was at its OMC found from compaction tests. Mixtures were mixed in electrical dough mixer for a complete uniformity, and then compacted in 10 equal layers in splitable cylindrical specially prepared PVC moulds which were securely tighten with steel clamps during compaction process. Each layer was given 56 blows from a laboratory made rammer which weighed 5.65 kg. Moulded precast columns were then oven dried at temperature of about 70°C. Dried columns were taken out of their moulds, and placed at the middle of the test tank while confined with the remoulded fibrous peat. In order to resemble the field condition for the precast columns, prior to load bearing capacity tests, the content of test tank was filled with water (saturated) for 24 hrs. Loading as well as unloading test procedures were conducted for plain reconstructed peat without column, and also for 300 mm column made of 15% OPC. The other five types of columns that had smaller diameter (200 mm) were subjected only to loading procedure.
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a)
b)
c)
d)
e)
f)
Figure 3.30: Load bearing capacity tests procedures: a) Compacting the stabilized sample in the mould, b) A moulded cement treated column, c) Moulded columns inside the oven, d) A precast stabilized column prior to be installed inside the test tank, e) Installed column in the test tank, and prior to be tested, f) Load bearing capacity test in progress 103
Also, finite element analysis using PLAXIS v8.2 has been carried out by using the shear strength parameters of the fibrous peat and stabilized columns.The shear strength parameters so calculated were utilized to simulate the plate load test and thus to have an idea about the effective stresses in the soil and the stabilized columns, and also to compare the deformations obtained from actual loading, with computerized model. The parameters required for peat and stabilized columns were, unit weight (γ), Poisson ratio (ν), Elastic modulus (E), cohesion (cu), friction angle (φu) and dilatancy angle (ψ). FEM analysis was carried out using Mohr-Coulomb’s criterion for soil and stabilized columns. As recommended by and Vermeer and Brinkgreve (1998), the angle of dilatancy was taken null for the plain peat. Drained behaviours for fibrous peat surrounding the columns, and undrained behaviour for the precast columns were assumed. Drainage was permitted from the top as was done during each actual test. The interface between the column and peat has been assumed to be rigid. The external loading applied at failure condition was same as in the actual load bearing capacity tests for plain (untreated) fibrous peat (Figure 3.31a), as well as plain fibrous peat reinforced with two types of OPC treated precast columns; 200 mm diameter (Figure 3.31b), and 300 mm diameter (Figure 3.31c). Their deformations at failure condition obtained from FEM analysis were compared with the actual values obtained during load bearing capacity tests.
Both precast columns of 200, and 300 mm in diameters used for FEM analysis purposes were identical in material contents and made from mixture of fibrous peat, and 15% ordinary Portland cement, and only difference between them was the size of their diameters.
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a)
b)
c)
Figure 3.31: FEM loading model for a) plain peat, b) Plain peat reinforced with 200 mm diameter column, c) Plain peat reinforced with 300 mm diameter column
3.12
Triaxial and Rowe cell tests on precast stabilized columns made of hemic and sapric peats
Consolidation undrained triaxial, and Rowe cell consolidation tests also have been conducted on hemic and sapric types of peats. Columns made of hemic and sapric peats were stabilized with 15% OPC, with and without two types of additives namely; polypropylene fibres and silica fume. Preparation of columns was identical to the procedure described for precast stabilized fibrous peat columns described earlier. Precast stabilized columns made of hemic and sapric peats were installed in undisturbed fibrous peat for triaxial and Rowe cell tests, and procedures conducting each test was identical to those procedures described in section 3.10 for precast stabilized peat columns made of fibrous peat as well. Hemic and sapric peats used for this research, were originated from the original fibrous peat that was used throughout this study as the main material. Preparing hemic and sapric peat was done using sieve
105
# 100, and procedure described in section 2.7.3 and in Table 2.3. Tests conducted on hemic and sapric peats included; sieve analysis, consistency limits, organic contents, SEM, EDX, and pH.
3.13
SEM and EDX tests on various types of materials
Scanning electron microscopy, and energy dispersing x – ray analysis tests have been conducted on the raw materials used in this research including; fibric, hemic, and sapric peats as well as ordinary Portland cement (OPC), blast furnace slag (BFS), fly ash (FA), and silica fume (SFU). The SEM tests were also conducted on OPC treated fibrous peat specimens, with and without additives for their structural bonding, and also to observe the micro-fabric changes which occurred before and after stabilization. SEM and EDX tests were conducted on various specimens using Oxford, INCA (JEOL JSM) instrument shown in Figure 3.32.
Figure 3.32: Oxford, INCA machine instrument used for SEM and EDX tests Preparing each specimen for testing included; placing a thin layer (tissue) from each sample over a double adhesive tape mounted on a metallic pad of about 10 mm in diameter, coating the specimen with a small amount of conductive material (Au) to carry away the charging electrons, and then placing them in the SEM, EDX viewing chamber for actual tests.
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3.14
Testing Programmes
Various types of tests have been conducted on different types of samples. These tests were conducted on raw materials such as plain fibrous peat samples, OPC, and additives, as well as OPC treated peat samples with or without additives. Table D2a through Table D3 in the appendix D show symbols, and descriptions for various types of samples used during testing programmes. The mentioned Tables depict the notations used for following Tables. Also Table D3 through D10 located in appendix D present different experiments carried out on various types of materials either at field or in laboratories (soil, water, and bioscience) during the course of the research.
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CHAPTER 4
RESULTS AND DISCUSSION
4.1
Introduction
This chapter presents the results of field and laboratory tests on fibrous peat which is located in western part of Selangor province in Malaysia. Soil samples used for the study obtained from several bore holes, and test pits at the same location within a radius of 20 m boundary. Also, this chapter presents discussions on graphed, and/or tabulated results acquired from laboratory test procedures that were carried out during the study, on untreated as well as treated fibrous peat samples using ordinary Portland cement (OPC) and various types of additives. Also after presentation of the results, there is a discussion on comparison between the obtained results of current study and past researches based on several factors including; strength values, materials costs, and the applicability of each method to the field is presented.
4.2
Results organization
The results presented in this chapter are divided in five main sections. Each section mainly represents the results obtained for each designated objective stated in chapter one. Also, the order of presentation complies with the order of objectives defined in chapter one as well. Each section and its subsections are representing the results of laboratory experiments carried out during the course of the study process. Also, each presented result is followed by a related discussion. The organization of this chapter includes the followings: 1- Evaluating the engineering properties of untreated fibrous peat as control measures 2- Air cured OPC treated fibrous peat strength gain versus conventional curing techniques 109
3- Strength gain of OPC treated fibrous peat when used with the following additives; a) Polypropylene fibres b) Silica fume c) Steel fibres d) Blast furnace slag e) Fly ash 4- Reinforcing fibrous peat with precast stabilized peat columns to increase load bearing capacity, and to reduce settlement of fibrous peat
4.2.1
Evaluating the engineering properties of untreated fibrous peat as control measures
Various types of tests were carried out at the field as well as in the laboratories in-order to find the engineering properties of peat used in the research that are explained in the following sections.
4.2.1.1
Field identification, and field vane shear tests
Identification tests using von Post technique (von Post and Granlund 1926) as well as odour, and colour tests on samples indicated that the soil was organic and classified as H 1 to H4. Ground water table (GWT) on rainy and hot days were fluctuating from 50 mm to 400 mm below surface level respectively. Based on the site investigation, and laboratory experiments soil profile for the field is presented in Figure 4.1.
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Figure 4.1: Ground subsurface profile Field vane shear tests values obtained for different depths are shown in Figure 4.2. This result indicate that; as depth increase within the peat boundary layer, the FVST values decrease, and that is possibly due to peat decomposition characteristics as well as increasing moisture contents.
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Field vane shear (kPa) 0
5
10
15
20
25
30
0 0.5
Depth (m)
1 1.5 2 2.5 3 3.5
Figure 4.2: FVS tests values versus depth 4.2.1.2
Laboratory tests on undisturbed and disturbed fibrous peat samples
In order to classify the soil, and confirming its field visual inspection laboratory tests including, sieve analysis (Figure 4.3), consistency tests, and fibre contents, have been conducted on the disturbed samples. A summarized tabulated results for the fibrous peat used in this study is also presented in Table 4.1.
According to the shape of grain size distribution curve for the peat used in the study shown in Figure 4.3, the soil is sandy type of soil, while in reality is peat. Therefore, it is essential to evaluate the particle size distribution curve of peat more cautiously, and always consider this result along with other engineering properties of the sieved soil.
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Figure 4.3: General particle size distribution of peat used in the research
Table 4.1: Properties of untreated peat
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4.2.2
Air cured OPC treated fibrous peat strength gain versus conventional curing techniques
OPC treated peat were tested for their strength using various types of curing methods that are explained with details in the following sections. 4.2.2.1
Effect of different curing techniques on the UCS values of stabilized fibrous peat samples
Three types of curing techniques have been used to cure identical UCS samples made of fibrous peat at fibrous peat’s natural moisture content (w = 189%) and different amount of OPC. Curing types used for the OPC treated samples were; moist curing, moist curing with surcharge load of 10 kPa, and air curing. Curing periods for the samples began from 0 day (after mixing) and continued up to 180 days.
UCS ( kPa)
The results are shown in Figure 4.4 through 4.6
800
0 day
700
m oist cured
600
m oist cured + 10 kPa surcharge load air cured
500 400 300 200 100 0
Undisturbed fibrous peat
5% OPC
15% OPC
30% OPC
50% OPC
Figure 4.4: UCS values vs. OPC treated samples for 28 days under different curing conditions
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0 day
1000 900
m oist cured
800
m oist cured + 10 kPa surcharge load air cured
UCS (kPa)
700 600 500 400 300 200 100 0
Undisturbed fibrous peat
5% OPC
15% OPC
30% OPC
50% OPC
Figure 4.5: UCS values vs. OPC treated samples for 90 days under different curing conditions
1200 1000
UCS (kPa)
800
0 day m oist cured m oist cured + 10 kPa surcharge load air cured
600 400 200 0 Undisturbed fibrous peat
5% OPC
15% OPC
30% OPC
50% OPC
Figure 4.6: UCS values vs. OPC treated samples for 180 days under different curing conditions It is observed from Figure 4.4 that all the samples, except with 50% OPC, show a higher UCS with air curing. With air curing, the UCS of samples containing 5, 15, and 30 and 50% OPC increased by a factor of 6 (22 to 135 kPa), 3 (47 to 136 kPa), 4 (100 to 500 kPa) and 3 (170 to 580 kPa) respectively at the end of 28 days compared with freshly prepared (0 day or after mixing) samples. Further, with moist 115
curing, the UCS of samples with 5 and 15% OPC decreased by a factor of 22 (22 to 1 kPa) and 1.5 (47 to 31 kPa) respectively, but for samples containing 30 and 50% OPC, it increased slightly by 13 and 25% respectively. Similarly, after moist curing along with surcharge load of 10 kPa, the UCS of samples containing 5, 15, 30, and 50% OPC increased by 5% (22 to 23 kPa), 17% (47 to 55 kPa), and a factor of over 3 (100 to 439 kPa) and 4 (170 to 720 kPa) respectively.
Also, amongst moist curing, moist curing with a surcharge load of 10 kPa and air curing techniques to stabilize fibrous peat, for 180 day curing period; (a) Air curing causes the UCS values of stabilized fibrous peat containing 5, 15, 30, and 50% ordinary Portland cement to increase by factors of 11 (from 28.5 to 310 kPa), 10 (from 28.5 to 295), 24 (from 28.5 to 695 kPa), and 26 (from 28.5 to 734 kPa), respectively, with 28.5 kPa being UCS value for undisturbed fibrous peat. (b) Moist curing plus a surcharge load of 10 kPa causes the UCS values of stabilized fibrous peat containing 15, 30, and 50% OPC to increase by factors of 2 (from 28.5 to 59 kPa), 21 (from 28.5 to 607), and 39 (from 28.5 to 1103 kPa), respectively, with 28.5 kPa being the UCS value for the undisturbed fibrous peat. (c) Moist curing alone causes the UCS values of stabilized fibrous peat containing 5% OPC to decrease by a factor of 17 (from 28.5 to 1.7 kPa) and containing 15, 30, and 50% OPC to increase by 34% (from 28.5 to 38.3 kPa), and a factor of 6 (from 28.5 to 175.5 kPa), and also a factor of 11 (from 28.5 to 315 kPa), respectively. d) Moist curing with surcharge load gives the highest UCS values when 50% OPC is used to stabilize fibrous peat for curing periods of 28, 90, and 180 days, compared with the two other curing techniques.
116
e) Moist curing alone gives the lowest UCS values for all stabilized fibrous peat containing 5 to 50% OPC for curing periods of 28, 90, and 180 days, compared with the other two curing techniques. f) As the curing period proceeds from 0 days (immediately after mixing) to 28, 90, and 180 days, the UCS values for air cured as well as for stabilized fibrous peat moist cured with a surcharge load of 10 kPa are increased. In general, the behaviour of samples as far as their UCS values are concerned at the end of 28, 90 and 180 days is very similar. Also, high dosage amount of OPC (50%) as well as constant compactive effort of surcharge load during curing period may be explained for higher strength gain of these types of stabilized samples. 4.2.3
Strength gain of OPC treated fibrous peat when used with various additives a) Polypropylene fibres b) Silica fume c) Steel fibres d) Blast furnace slag e) Fly ash
4.2.3.a1
Effect of propylene fibres in strengthening OPC treated fibrous peat
Polypropylene fibres (PPF) as an additive was used in OPC treated fibrous peat samples, and its effect was evaluated through UCS, and CBR tests. Air curing technique was used to cure the OPC treated fibrous peat samples with PPF. Optimum dosage rate of PPF in the samples was determined through trial and error experiments. Soaking samples to 100% saturation test was also conducted to measure the
117
time length that how long an OPC treated fibrous peat sample needs to be submerged in water to reach complete saturation. In the following sections, the results of these tests are presented.
4.2.3.a2
Optimum polypropylene fibres (PPF) dosage rate determination
The amount of fibres to be used for this study was decided based on the results of unsoaked, 90 days air cured UCS, and CBR tests. Figure 4.7 shows the results of the UCS tests expressed in increase ratio (%) versus various amount of OPC, used with different dosage rate of polypropylene fibres. The original peat used to make samples for UCS tests (15, 25, and 30% OPC treated peats) were originated from various depths, and had different moisture contents and also were different in type (H 1 to H4) as well. As the results expressed in increase ratio and shown in Figure 4.7 indicate a fibre content of 0.15% give the highest UCS values for all three types of OPC treated peats (15, 25, and 30%).
Results obtained from UCS tests were confirmed by unsoaked CBR tests conducted on fibrous peat stabilized with 5, 15 and 25% OPC and 0.1, 0.15, and 0.2% fibres and air cured for 90 days. All the peat samples used for CBR tests unlike the UCS test samples described earlier were from exact location, and contained similar moisture contents. CBR values as well as increase ratios for tested samples are given in Figure 4.8. The results in this Figure confirms the results obtained for UCS tests shown on Figure 4.7, that 0.15 % polypropylene fibres when used with various amount of OPC treated fibrous peats provide higher strength values.
From the results on both Figures, it may be concluded that when less than 0.15% polypropylene fibres used, less strength gained, possibly due to insufficient fibres, while when more than 0.15% polypropylene fibres are used less strength is gained possibly due to higher amount of fibres that are not uniformly distributed within the treated peat samples. 118
Basically, the increase ratio values expressed in percent presented in this section were calculated using the following relation: (Obtained UCS for each type of sample/Max. UCS values obtained among samples) ×100
UCS increase ratio (%)
100 80 60 40 20
P
0. 15 %
0. 10 %
P
PF +1 5% O
PC PF +F ib +1 .P 0. 5 % t 20 O % P P C PF +F ib +1 .P 0. 5% t 10 O % PC P PF +F ib +2 .P 5 0. % t 15 O % PC P PF +F ib +2 .P 5% 0. t 20 O % P P C PF +F ib +2 0. .P 5 10 % t O % P P C PF +F +3 ib 0 .P 0. % t 15 O % PC P + PF Fi +3 b. Pt 0% 0. O 20 PC % +F P PF ib .P +3 t 0% O PC +F Pt
0
Figure 4.7: UCS increase ratios (%) vs. different amount of different amount of ordinary Portland cement, with various dosage rate of polypropylene fibres (air cured for 90 days)
119
CBR values
100
40
80
30
60
20
40
10
20
0
0
CBR increase ratio (%)
CBR ratios
0. 1% PP F+ 0. 5% 15 OP % PP C +F F +5 ib 0. % .P 5% OP t PP C +F F+ ib 0. 5% 1% .P O t PP PC F+ +F 0. 15 ib 15 % .P % O t PP PC F + +1 Fi 0. b 5% 5% .P O t PP PC F+ +F 15 0. ib 1% % .P O t PP PC F+ +F 0. 25 ib 15 % .P % O t PP PC F +F +2 ib 0. 5% 5% .P O t PP PC F+ +F 25 ib % .P OP t C +F ib .P t
Actual CBR (%)
50
Figure 4.8: Percent increase and actual CBR values vs. different amount of ordinary Portland cement, with various dosage rate of polypropylene fibres (air cured for 90 days) 4.2.3.a3
Least soaking period to saturate stabilized samples
The stabilized CBR samples compacted at their optimum moisture contents containing 50% OPC and 0.15% fibres and air cured for three months were chosen for the soaking procedure and were soaked for three weeks. The results of this test that is shown in Figure 4.9 indicate that the samples reach their constant weight or 100% saturation at the end of seven days. Therefore, based on this result, all the stabilized peat samples (5, 10, 15, 30, and 50% ordinary Portland cement with and without additives) were submerged in water for seven days before carrying out UCS and/or CBR tests under soaked condition on them.
120
Weight increase (%)
100 80 60 40 20 0 0
3
6
9
12
15
18
21
Soaking duration (days)
Figure 4.9: Percentage weight increase vs. time for soaked CBR samples 4.2.3.a4
UCS and CBR values of OPC and polypropylene fibres (PPF) treated fibrous peat using peat’s natural moisture content
Different types of UCS tests samples made of fibrous peat that had a moisture content of 198% and various amount of OPC (5,15,20, 30, and 50%), and 0.15% PPF were prepared, and then cured through time and up to 90 days. UCS tests were then conducted for stabilized samples immediately after mixing (0 day), 7, 28, and 90 days. Soaked UCS tests were also conducted on 90 days air cured samples by submerging them in water for 7 days prior to be tested as soaked samples. The results are shown in Figure 4.10 through Figure 4.14. Also, UCS tests were conducted on plain (untreated) fibrous peat samples immediately after mixing (0 day), and after 90 days, in unsoaked (cured in air), and soaked (cured 90 days in air, and then soaked for 7 days). The result is shown in Figure 4.15.
121
Fpeat+5%cement
Fpeat+5%cement+0.15%PPF
Fpeat+5%cement(soaked)
Fpeat+5%cement+0.15%PPF(soaked)
500
UCS (kPa)
400 300 200 100 0 0
10
20
30
40
50
60
70
80
90
100
Curing Time (days)
Figure 4.10: Unconfined compressive strength (UCS) values for fibrous peat and 5% OPC with and without polypropylene fibres (PPF) vs. curing time
Fpeat+15%cement
Fpeat+15%cement+0.15%PPF
peat+15%cement(soaked)
peat+15%cement+0.15%PPF(soaked)
UCS (kpa)
300 200 100 0 0
10
20
30
40 50 60 Curing Time (days)
70
80
90
100
Figure 4.11: Unconfined compressive strength (UCS) values for fibrous peat and 15% OPC with and without polypropylene fibres (PPF) vs. curing time
122
Fpeat+20%cement
Fpeat+20%cement+0.15%PPF
Fpeat+20%cement(soaked)
Fpeat+20%cement+0.15%PPF(soaked)
UCS (kPa)
300 200 100 0 0
10
20
30
40
50
60
70
80
90
100
Curing Time (days)
Figure 4.12: Unconfined compressive strength (UCS) values for fibrous peat and 20% OPC with and without polypropylene fibres (PPF) vs. curing time
600
Fpeat+30%cement
Fpeat+30%cement+0.15%PPF
Fpeat+30%cement(soaked)
Fpeat+30%cement+0.15%PPF(soaked)
UCS (kPa)
500 400 300 200 100 0 0
10
20
30
40 50 60 Curing Time (days)
70
80
90
100
Figure 4.13: Unconfined compressive strength (UCS) values for fibrous peat and 30% OPC with and without polypropylene fibres (PPF) vs. curing time
123
Figure 4.14: Unconfined compressive strength (UCS) values for fibrous peat and 50% OPC with and without polypropylene fibres (PPF) vs. curing time
plain fibrous peat(unsoaked)
fibrous peat+0.15%PPF(unsoaked)
plain fibrous peat(soaked)
fibrous peat+0.15%PPF(soaked)
UCS (Kpa)
400 300 200 100 0 0
10
20
30
40
50 60 Time (days)
70
80
90
100
Figure 4.15: UCS values of various types of plain fibrous peat vs. curing period
124
Results obtained from Figures 4.10 to 4.15 include; a) As the OPC amount is increased in stabilized samples with or without PPF, the immediate (0 day) and soaked UCS values increase as well. b) Addition of 0.15% polypropylene to the OPC treated fibrous peat samples adds additional UCS values of the air cured stabilized samples. c) UCS values increase from 28 days to 90 days of curing periods for samples containing 5% OPC by over 142% (from 128 to 310), and 196% (from 135 to 400), and for 15% by over 135% and 196%, and also for samples containing 30% OPC by 5% (from 400 to 420 kPa) and 7% (300 to 320 kPa) with and without PPF respectively. d) UCS of 15% OPC treated stabilized fibrous peat cured for 90 days increases by a factor of 7 (from 28.5 to 190 kPa), inclusion of 0.15% polypropylene increases the UCS further by a factor of over 9 ( from 28.5 to 280 kPa). Also, their soaked values increase by a factor of 3 (from 28.5 to 85 kPa), and 4 (from 28.5 to 115 kPa) without and with fibres, respectively. e) In general soaking process of stabilized samples causes the UCS values of the respective unsoaked samples to drop. As the cement amount in the samples increase the size of this drop is less considerable
From the obtained results, it is also possible to conclude that; stabilizing fibrous peat with OPC at its field moisture content increases the UCS value during curing. In general, for lower dosage of cement content stabilized fibrous peat, the slope of the curve up to 28 days is less than the slope beyond 28 days, but for the higher dosage cement content (30, and 50% OPC) samples that is reversed. The reason may be due to the possibility that as cement contents of the samples are increased to higher amounts (30%, and specially 50% OPC) more strength is gained through first 28 days, and the stabilized samples may behave similar to the behaviour of cement mortar mixes (cement, sand and water) which they gain most of their strength within first 28 days (Neville 1999). 125
Also, the results obtained from UCS values for plain fibrous peat with, and without PPF cured for 90 days and tested as unsoaked, and soaked samples shown in Figure 4.15 indicate that; plain fibrous peat treated with, and without PPF gain UCS values in 90 days of air curing period by factors of 8 (from 28.5 to 240), and 6 (from 28.5 to 170 kPa) respectively. Soaking the identical air cured fibrous samples on the other hand have resulted the UCS value of fibrous peat with fibres to drop by factor of 6 (from 240 to 39 kPa), and the sample without fibres loses all of its strength (from 170 to 0 kPa) when soaked.
Also, Figure 4.16 shows the reduction of moisture contents for various types of treated peat samples through air curing period from just after mixing and up to 90 days. Comparing the results of treated peat samples having various amount of OPC in this Figure indicate that stabilized samples containing 5% ordinary Portland cement continue to lose moisture contents with a faster rate than other type of stabilized samples, and with a sharper slope during the curing periods. The final moisture content of samples with 5% OPC at the end of 90 days curing period is close to stabilized samples treated with 30% OPC. At the same time, if the 90 days cured UCS (unsoaked) values of samples with 5% OPC shown in Figure 4.10, is compared with other results shown in Figures 4.11, 4.12, 4.13 belonging to stabilized peat samples containing 15, 20, and 30% OPC respectively, it is possible to observe that the unsoaked UCS values of samples having only 5% OPC is relatively higher than those samples having more OPC contents. This phenomenon may be explained by the fact that; as the treated fibrous samples lose their moisture contents through air curing periods, they gain strength because of their wooden fibre contents. And according to Figure 4.16, this condition is more relevant to samples containing less amount of OPC (5%). As these woody fibres that make most of the structural identity of fibrous peat lose their moistures, and become drier, the samples become more solid and thus gain more strength. And, as soon as the stabilized samples containing less amounts of OPC, namely samples with 5% (Figure 4.10) or 126
0% (Figure 4.15) OPC are soaked, their gained strengths drop by significant amounts, and their actual strengths are revealed.
Figure 4.16: Moisture contents reductions versus curing periods for various types of treated fibrous peat samples Also CBR tests were conducted on various types of OPC treated fibrous peat for their unsoaked as well as soaked CBR values. The CBR samples first were air cured for three months, and then tested under unsoaked and soaked conditions. Figure 4.17 shows their obtained results. The results indicate that; a) For stabilized fibrous peat with 15% OPC and cured for 90 days, the unsoaked and soaked CBR increase by factors of over 23 (from 0.8 to 19%), and 9 (from 0.8 to 7.2%), respectively b) For stabilized fibrous peat with 15% OPC, 0.15% polypropylene fibres and cured for 90 days, the unsoaked and soaked CBR increase by factors of over 28 (from 0.8 to 23), and over 18 (from 0.8 to 15).
127
Three months of air curing technique as well as 15% OPC and 0.15% polypropylene fibres used to stabilize fibrous peat will increase the general rating of the in-situ peat from very poor (CBR from 0 to 3%) to fair and good (CBR from 7 to above 20%) [Bowles 1978].
The peat samples stabilized with OPC and polypropylene fibres show an increase in CBR values by as high as 39% (with 50% OPC). The OPC acts as a binding agent and is responsible for the increase in the mechanical strength of the samples. When cement and water are mixed together, the aluminates reacts with the water to form an aluminate-rich gel which reacts with sulfate in solution and the cement start to hydrate, with the formation of calcium silicate hydrate and calcium hydroxide and it gains strength. The polypropylene fibres act as reinforcements to the fibrous peat. It appears that it prevents the formation of cracks in the sample and along with cement, binds the peat particles together, leading to an increase in CBR values of the stabilized peat samples. The results agree well with the findings of researchers (Sivakumar et al. 2008: and Tang et al. 2007) who have also reported an increase in strength with the addition of cement and polypropylene fibres in clay.
There appears to be some micro-structural changes resulting from the addition of cement and polypropylene fibres or the interaction between cement and fibre reinforcement which is responsible for the increase in UCS, as well as CBR values. The air curing technique for curing the stabilized peat samples, instead of normal moist curing also plays an important role in increasing the strength as this method keeps lowering the moisture contents, and as the moisture contents reduce, stabilized samples gain more strength as well.
128
40
unsoaked
CBR (%)
30
soaked
20 10
Fp
Fp
Un
di s. fib ro u
s
pe at
t+ t+ 5% 5% OP OP C C +0 .1 5% PP Fp Fp F t+ t+ 1 15 5 % % OP OP C C +0 .1 5% PP Fp Fp F t+ t+ 30 30 % % OP OP C C +0 .1 5% PP Fp Fp F t+ t+ 50 50 % % OP OP C C +0 .1 5% PP F
0
Figure 4.17: CBR (%) values for the undisturbed peat and different percentage of OPC and polypropylene fibres for the stabilized peat cured for 90 days
4.2.3.a5
Use of OPC, PPF and optimum moisture content (OMC) values to strengthen fibrous peat
Compacting the mineral soils under their OMC will usually provide their maximum strength gained under normal condition. Following this character of mineral soils, this section of the study involved mixing fibrous peat samples with different amounts of OPC, with or without PPF, compacting them at their respective optimum moisture content found from compaction tests, and curing them in air for 90 days. To evaluate the mechanical behaviour of the stabilized peat samples, California bearing ratio (CBR) tests were performed under two conditions, unsoaked and soaked. CBR tests were carried out on plain fibrous peat, and plain fibrous peat inclusive of 0.15% polypropylene fibres as control measure samples. CBR tests were also carried out on fibrous peat stabilized with various amounts of OPC with or without 0.15% PP fibres.
129
Unsoaked CBR tests were carried out on samples air cured for 1, 28, and 90 days while soaked CBR tests were carried out on samples air cured for 90 days. The amounts of ordinary Portland cement used for the stabilized CBR samples were 5, 10, 15, 20, 30 and 50%.
Compaction tests results presented in Figure 4.18a, and 4.18b that have been used to make CBR samples show that as the amount of OPC in the mixture of fibrous peat and OPC is increased, the values for dry unit weights increase and the OMC decreases. Also, as the fibres are added to each set of peat mixtures, the OMC decreases and their respective dry unit weights of the mix increases. However, the decrease in OMC and the increase in the dry unit weight of the mixtures containing fibres are very slight when compared with mixtures without fibres.
130
a)
b)
Figure 4.18: Dry density-moisture curves: (a) Untreated fibrous peat and fibrous peat stabilized with cement (b) Treated fibrous peat with PP fibre only and fibrous peat stabilized with cement and PP fibres
131
The CBR values obtained for plain fibrous with, and without fibres as well as fibrous peat stabilized with fibres and air cured for 1, 28 and 90 days are shown in Figure 4.19. The results from Figure 4.19 indicate that; a) As the curing period increases, the CBR values increase as well b) With the increase in OPC content from 0 to 50%, the CBR values are also increasing c) Addition of 0.15% fibres to the OPC treated peat samples increases the CBR values over samples without fibres further
The results show that the CBR increases from 0.8% for undisturbed fibrous peat to 145% for peat stabilized with 50% OPC and 0.15% fibre (CBR obtained using natural moisture content gave 39%, shown in Figure 4.17). This significant increase in CBR values compared with the obtained CBR values from using natural moisture content of the fibric peat can be attributed to the OMC at which the samples were compacted to their maximum dried densities found from compaction curves. Results shown in Figure 4.19 indicate that curing period has a significant effect on the CBR strength of the stabilized peat samples as it had for all stabilized peat samples described earlier.
The results of soaked CBR values obtained for stabilized peat that have been air cured for 90 days are presented in Figures 4.19, and 4.20. These results indicate that; a) the soaked stabilized peat samples with ordinary Portland cement gain strength through 90 days of curing period, and inclusion of polypropylene fibres adds more to their gain of strength. b) The unsoaked and soaked CBR values of stabilized fibrous peat treated with 15% OPC and cured for 90 days increase by factors of 75 (from 0.8 to 60.4%), and 27 (from 0.8 to 22%) compared with the CBR of undisturbed fibrous peat.
132
c) The unsoaked and soaked CBR values of stabilized fibrous peat treated with 15% OPC and 0.15% polypropylene fibres and cured for 90 days increase by factors of over 79 (from 0.8 to 63.5%), and 35 (from 0.8 to 28.2%) compared with the CBR of undisturbed fibrous peat.
Soaked strength gain for samples without OPC (with 0% OPC and 0.15% PPF) obtained from Figure 4.19, and 4.20 indicate that a significant strength drops compared with the unsoaked samples obtained from 44.3 to 4%. This proves that use of ordinary Portland cement as a binding agent is an important factor to increase the strength of fibrous peat. The CBR values at OMC confirm the previous finding for the strength values obtained with the natural moisture content of fibrous peat that, as the curing period or OPC content is increased, the CBR values increase as well. In addition, the inclusion of polypropylene fibres adds further to the strength.
160
1 day(with no PPF)
28 days(with no PPF)
140
90 days(with no PPF)
1 day (with PPF)
120
28 days (with PPF)
90 days (with PPF)
CBR (%)
100 80 60 40 20 0 0
5
10
15 OPC content (%)
20
30
50
Figure 4.19: Unsoaked CBR values for stabilized fibrous peat samples treated with 0.15% Polypropylene fibres and different amount of ordinary Portland cement at different air curing periods
133
160 140
90 days(w ith no PPF)
CBR (%)
120
90 days (w ith PPF)
100 80 60 40 20 0 0
5
10
15
20
30
50
OPC content (%)
Figure 4.20: Soaked CBR values air cured at 90 days for stabilized fibrous peat with various amount of ordinary Portland cement, and 0.15% polypropylene fibres Results from Figure 4.21 for the SEM analysis tests on plain fibrous peat (Figure 4.21a), as well as stabilized fibrous peat with 5% OPC and 0.15% PPF (Figure 4.21b), fibrous peat with 15% OPC and 0.15% PPF (Figure 4.21 c), and fibrous peat with 30% OPC and 0.15% PPF (Figure 4.21d), indicate that; polypropylene fibres when used in OPC treated fibrous peat as additive will increase the bindings of the particles in general as well as inner coherent of the formed blocks in particular. Also as the OPC content or binding agent amount is increased in the stabilized samples there is a reduction in voids, and the micro structures of the samples are become more intact due to hydration process.
134
a)
b) Voids
c)
d) Voids
Figure 4.21: Scanning electron micrograph of: a) original plain fibrous peat, b) stabilized fibrous peat with 5% OPC, and 0.15% PPF, c) stabilized fibrous peat with 15% OPC, and 0.15% PPF, d) stabilized fibrous peat with 30% OPC, and 0.15% PPF Visual inspection of stabilized peat samples after each test confirmed the SEM results shown in Figure 4.21, and indicated that the samples containing higher OPC appeared to be more uniform and intact. Addition of the fibres to the samples caused the stabilized samples to be even more uniform and intact with fewer and smaller cracks as well.
135
Figure 4.22 shows examples of stabilized CBR samples containing PP fibres, with those which did not. The samples compared for this purpose had similar OPC contents.
Figure 4.22: Degree of intactness in cement treated CBR samples with (L), and without inclusion of polypropylene fibres (R) reinforcements
4.2.3.b1
Effect of silica fume (SFU) or micro silica in strengthening OPC treated fibrous peat
Silica fume (SFU) or micro silica as an additive was used in OPC treated fibrous peat samples, and its effect was evaluated through UCS, and CBR tests. Air curing technique was used to cure the samples with SFU. Optimum dosage rate of SFU in the samples was determined through trial and error experiments. In the following sections, the results of these tests are presented.
136
4.2.3.b2
Optimum silica fume (SFU) dosage rate determination
In this study, in order to determine the optimum percentage of silica fume content for the stabilized fibrous peat that would give the maximum strength values for unconfined compressive strength as well as California bearing ratio, fibrous peat samples at their natural moisture contents were mixed with 5% and 10% silica fume with different percentages of OPC. The samples that showed the maximum strength values for unconfined compressive strength as well as for the California bearing ratio were chosen as the optimum silica fume dosage rate for further study of stabilized fibrous peat.
Figure 4.23 shows the results of UCS tests for 5%, and 10% silica fume when used with various amounts of ordinary Portland cement for samples air cured for 90 days. It is observed that the silica fume at 10% dose gives higher UCS with 5 to 15% cement but with a cement content of 20 to 50%, a lower dose of silica fume at 5% gives higher UCS result.
Also, the results of CBR test samples cured for 90 days are shown in Figure 4.24 along with the percentage increase as well as the actual values of CBR with 15 and 25% of cement and 5 and 10% of silica fume. It is observed that with 15% cement, 10% silica fume higher CBR value but samples with 25% cement, 5% silica fumes gives higher CBR values which confirms the results of UCS values shown in Figure 4.23.
137
5%SFU(%ratio)
10%SFU(%ratio)
5%SFU (actual UCS)
10%SFU(actual UCS) 700 600
80
500 60
400 300
40
200 20
UCS actual value (kPa)
UCS increase ratio (%)
100
100
0
0 5
15
25 OPC content (%)
40
50
100
CBR values (%)
40
80
30
60
20
40
0 PC +1 0% SF FP t+ 25 % O
FP t+ 25 % O
PC +1 0% SF FP t+ 15 % O
FP t+ 15 % O
U
0 PC +5 % SF U
10
U
20
Actual CBR (%)
CBR ratios (%)
PC +5 % SF U
CBR increase ratio (%)
Figure 4.23: Percentage increase in UCS/actual UCS values versus different percentages of ordinary Portland cement and silica fume
Figure 4.24: Percentage increase in CBR/actual CBR values versus different percentages of ordinary Portland cement and silica fume
138
4.2.3.b3
UCS and CBR values of OPC, and silica fume (SFU) treated fibrous peat using peat’s natural moisture content
Different types of UCS tests samples made of fibrous peat that had a moisture content of 187% and various amount of OPC (5,15, and 25%), and with their optimum (most effective) dosage rate of SFU (5, and 10%) were prepared, and then air cured through time up to 90 days. UCS tests were then conducted for stabilized samples. Soaked UCS tests were also conducted on 90 days air cured samples by submerging them in water for 7 days prior to be tested as soaked samples. The results are shown in Figure 4.25.
500
un-soaked
UCS (kPa)
400
soaked
300 200 100
FU S
PC O
PC
+5 %
O FP t+ 25 %
+1 0% PC O
FP t+ 15 %
FP t+ 25 %
SF U
PC O
FU
FP t+ 15 %
PC +1 0% S
PC
O
O 5% FP t+
FP t+ 5%
U
nd is .fi br ou
s
pe at
0
Figure 4.25: UCS values for different percentages of ordinary Portland cement and silica fume for unsoaked and soaked samples
From the results of UCS test (Figure 4.25), it is observed that; a) Use of 10% silica fume in three months air cured, 15% OPC treated stabilized
fibrous peat
increases the unsoaked and soaked UCS values by 10% (from 300 to 330 kPa) and 72% (from 96 to 165 kPa), respectively, compared with when it is stabilized with only 15% OPC. b) UCS values of the samples increases with the increase in cement content. 139
c) 5% silica fume along with 25% OPC has caused the 90 days UCS of unsoaked,
and soaked
stabilized samples to increase by 15% (from 332 to 381 kPa), and 17% (from 268.5 to 315 kPa) respectively. d) Dosage rates of 5, 15 and 25% of OPC along with 5 and 10% of silica fume increase the soaked UCS values of undisturbed fibrous peat by a factor of as high as 10. From result shown in Figure 4.26, curing stabilized peat in air for 90 days with 5% OPC and 10% silica fume increases the CBR values of in-situ peat by a factor of more than 23 and 7 (from 0.8% to 18.6% and 5.7% ) for unsoaked and soaked samples respectively. Also, use of 10% silica fume in three months air cured, 15% OPC treated stabilized fibrous peat increases the unsoaked and soaked CBR values by 22% (from 24 to 29.4 %) and 35% (from 11.5 to 15.5%), respectively, compared with when it is stabilized with only 15% OPC.
35
un-soaked
CBR (%)
30
soaked
25 20 15 10 5
FU % S
PC O
PC
+5
O FP t+ 25 %
PC O
FP t+ 25 %
FU +1 0% S
PC O FP t+ 15 %
FP t+ 15 %
FU PC +1 0% S O
PC O FP t+ 5%
FP t+ 5%
U
nd is .fi br ou
s
pe at
0
Figure 4.26: CBR values for different percentages of ordinary Portland cement and silica fume for unsoaked and soaked samples Soaked samples compared with unsoaked samples show drops in their UCS, as well as CBR values. As the OPC contents of the samples are increased the amounts of drops decrease. 140
4.2.3.b4
Use of OPC, silica fume (SFU) and optimum moisture content (OMC) values to strengthen fibrous peat
Ordinary Portland cement along with the most effective dosage rates of silica fumes were used to evaluate the strength of stabilized fibrous peat through CBR (unsoaked and soaked) tests. CBR samples for this purpose were prepared by using OMC obtained from compaction tests shown in Figures 4.18a, and 4.27. CBR samples were tested at 1, 28, and 90 days of being air cured. Also soaked CBR tests were conducted on samples that were cured for 90 days.
Amount of ordinary Portland cement used for the CBR tests were 5, 10, 15, and 30% along with either 5, or 10% silica fume, as specified in section 4.6.1. The results of CBR tests on unsoaked stabilized samples are presented in Figure 4.28, and soaked in Figure 4.29. The results indicate that; a) The unsoaked and soaked CBR values of stabilized fibrous peat treated with 15% OPC and 10% silica fume and cured for 90 days increase by factors of over 85 (from 0.8 to 68.4%), and 30 (from 0.8 to 24.2%), compared with the CBR of undisturbed fibrous peat. b) Use of 5% silica fume in 30% OPC treated stabilized fibrous peat increases the unsoaked and soaked CBR values by 29.4% (from 71 to 91.9 %) and 34.8% (from 40.2 to 48.5%), respectively, compared with when they are stabilized with only 30% OPC. Results shown in Figure 4.28, for 30% OPC treated samples with, and without silica fume indicate that; sample without silica fume gives higher CBR values up to 28 days, but at 90 days the sample with silica fume has a higher CBR value. This indicates that silica fume when used with higher dosage of OPC treated fibrous peat makes the stabilized peat to be late setting. Based on the results shown in Figure 4.28 unsoaked CBR value for 5% OPC, and 10% silica fume treated fibrous peat reaches to 76% during 90 days of curing period, but it drops to 4.6% when soaked. This indicates that; fibrous peat when treated with less OPC, at their OMC can gain a significant 141
strength through drying conditions, but when they are back saturated, they lose most or all of their strength. Also, from the results shown in Figure 4.29 which compares soaked 90 days stabilized samples without, and with silica fume, it is possible to observe that, there is an increase of over 11% for CBR sample containing 15% OPC and silica fume with the identical sample without silica fume (from 22 to 24.5%).
Figure 4.27: Dry density-moisture curves, for treated fibrous peat with different amount of ordinary Portland cement, and silica fume
142
90
5%OPC
80
10%OPC
15%OPC
30%OPC
70 CBR (%)
60 50 40 30 20 10 0 1 day(w ith no 28 days(w ith 90 days(w ith SFU) no SFU) no SFU)
1 day(w ith SFU)
28 days(w ith 90 days(w ith SFU) SFU)
Figure 4.28: CBR values for treated fibrous peat with 5, and 10% silica fume, and various amount of ordinary Portland cement cured for 1, 28, and 90 days (unsoaked)
45
90 days(with no SFU)
90 days(with SFU)
40 35
CBR (%)
30 25 20 15 10 5 0 5
10
15
30
OPC content (%)
Figure 4.29: Soaked CBR values air cured at 90 days for stabilized fibrous peat with various amount of ordinary Portland cement, and silica fume
143
4.2.3c
Effect of steel and polypropylene fibres (StF, and PPF) to strengthen OPC treated fibrous peat
This section describes a laboratory study on stabilizing fibrous peat using ordinary Portland cement (OPC), as binding agent, and also steel fibres, as well as joint use of polypropylene and steel fibres as additives. Type of strength evaluation tests used in the study were unconfined compressive strength (UCS), and California bearing ratio (CBR). Compaction curves shown in Figure 4.18 were used to construct UCS, and CBR samples. Optimum moisture contents values used for all samples containing 5% OPC were 109 ± 1%, and samples containing 15% OPC, were 89.5 ± 1.5%, and also for samples containing 30% OPC were 82 ± 1%.
UCS tests samples were cured for three months, and CBR test samples were cured for 1, 28, and 90 days. All three months old samples either for UCS, or CBR tests were tested under two unsoaked and soaked conditions.
Dosage rates of OPC used for UCS samples were 5, and 15%, while for the CBR samples were 5, 15, and 30%. Polypropylene dosage rate used was 0.15%, and steel fibres amounts used in the study were 2, and 4%. Results obtained from unconfined compressive strength values on stabilized peat samples that were compacted at their optimum moisture contents and air cured for three months (soaked, and unsoaked) shown on Figure 4.30, and Figure 4.31, include; a) Use of 0.15% polypropylene fibres or 2% steel fibres in the mixture of peat and OPC, cause the UCS values (soaked, and unsoaked) of the stabilized peat samples to increase compared with when only plain peat is used. b) 0.15% Polypropylene fibres when used in the mixture of stabilized peat samples alone, is more effective to increase the UCS values of soaked samples than when only 2% steel fibres is used in the mixture of stabilized peat samples. 144
c) The unsoaked and soaked UCS values of stabilized fibrous peat treated with 5% OPC and 2% steel fibres and cured for 90 days increase by factors of over 11 (from 28.5 to 332 kPa), and 4 (from 28.5 to 116.8 kPa), respectively, compared with the UCS of undisturbed fibrous peat. d) The unsoaked and soaked UCS values of stabilized fibrous peat treated with 5% OPC (about 50kg/m3), 2% steel fibres (about 20 kg/m3) and 0.15% polypropylene fibres (about 1.5 kg/m3) and cured for 90 days increase by factors of over 27 (from 28.5 to 772.5 kPa), and 9 (from 28.5 to 256.8 kPa), respectively, compared with the UCS of undisturbed fibrous peat. e) The unsoaked and soaked UCS values of stabilized fibrous peat treated with 15% OPC, 2% steel fibres and cured for 90 days increase by factors of over 18 (from 28.5 to 523 kPa), and 7 (from 28.5 to 209.5 kPa), respectively, compared with the UCS of undisturbed fibrous peat. f) The unsoaked and soaked UCS values of stabilized fibrous peat treated with 15% OPC, 2% steel fibres, and 0.15% polypropylene fibres and cured for 90 days increase by factors of over 26 (from 28.5 to 746 kPa), and 12 (from 28.5 to 354.8 kPa), respectively, compared with the CBR of undisturbed fibrous peat. g) As the OPC content of the stabilized peat samples increases, the UCS values (soaked, and unsoaked) increase as well. h) Soaking condition of the stabilized samples causes the UCS to drop compared with the UCS values of the corresponding unsoaked samples. i) Less decrease in soaked UCS values for those samples that contained more OPC content as well those samples containing polypropylene fibres, from their corresponding unsoaked UCS values.
145
Figure 4.30: Unsoaked and soaked unconfined compressive strength values for fibrous plain peat and fibrous peat (FPt) with 5% cement ordinary Portland cement (OPC) with and without 0.15% of polypropylene fibres (PPF), as well as 2% steel fibres (StF) cured for three months
Figure 4.31: Unsoaked and soaked unconfined compressive strength values for fibrous peat plus 15% ordinary Portland cement (OPC) with and without 0.15% of polypropylene fibres (PPF), as well as 2% steel fibres (StF) cured for three months
146
Results obtained from CBR tests conducted on stabilized peat samples compacted at OMC, containing 0, to 30% OPC, with and without polypropylene fibres and steel fibres that were air cured for: 24 hrs, 28 days and three months shown on Figure 4.32, Figure 4.33, and Figure 4.34 respectively include; a) As the OPC amounts in the stabilized peat samples are increased, the CBR values increase as well b) As the curing period is continued, CBR values increase c) Use of polypropylene fibres or steel fibres in the mixture of stabilized peat samples cause the CBR values to increase compared with CBR of plain peat d) Joint use of polypropylene fibres and steel fibres will cause the stabilized peat samples to increase further compared with when only one of them is used e) As the OPC amount in the mixture of stabilized peat samples is increased CBR values for unsoaked and soaked samples increase as well. f) Soaking condition of the stabilized samples causes the CBR values to drop compared with the CBR values of the corresponding unsoaked samples g) Less drop in CBR values for soaked samples are detected from their unsoaked CBR values for those samples containing more OPC amount, as well as for those samples that contained polypropylene fibres h) As the steel fibres amount in the mixture of stabilized peat samples is increased from 2 to 4%, the unsoaked and soaked CBR values are increased as well Also some quantitative results obtained from Figures 4.33 to 4.35 include; a) The unsoaked and soaked CBR values of stabilized fibrous peat treated with 5% OPC and 4% steel fibres and cured for 90 days increase by factors of over 70 (from 0.8 to 56.7%) and 17 (from 0.8 to 13.7%), respectively, compared with the CBR of undisturbed fibrous peat. b) The unsoaked and soaked CBR values of stabilized fibrous peat treated with 5% OPC, 2% steel fibres, and 0.15% polypropylene fibres and cured for 90 days increase by factors of over 84 147
(from 0.8 to 67.8%) and 19 (from 0.8 to 15.5%), respectively, compared with the CBR of undisturbed fibrous peat. c) The unsoaked and soaked CBR values of stabilized fibrous peat treated with 15% OPC and 4% steel fibres and cured for 90 days increase by factors of over 87 (from 0.8 to 70%) and 43 (from 0.8 to 34.6%), respectively, compared with the CBR of undisturbed fibrous peat. d) The unsoaked and soaked CBR values of stabilized fibrous peat treated with 15% OPC, 4% steel fibres and 0.15% polypropylene fibres and cured for 90 days increase by factors of over 97 (from 0.8 to 78%) and 50 (from 0.8 to 40.4%), respectively, compared with the CBR of undisturbed fibrous peat.
Figure 4.32: CBR values of fibrous plain peat samples, as well different types of stabilized peat samples containing 0.15% polypropylene fibres (PPF) and 2 or 4% steel fibres (StF) with 5% OPC, cured for 1, 28 (unsoaked), and 90 days (unsoaked, and soaked)
148
CBR (%)
100 75
unsoaked - 24 hours
unsoaked - 28 days
unsoaked - 3 months
soaked - 3 months
50 25 0 5% O t+ 1 P F
PC
t+ FP
O 15%
PC +
PF %P 5 1 0.
5% t +1 P F
% .15 0 + C OP
tF %S 2 + F PP
5% t +1 P F
tF %S 4 + C OP
5% t +1 P F
% .15 0 + C OP
tF %S 4 + F PP
Figure 4.33: CBR values of different types of stabilized fibrous peat samples containing 15% cement with 0.15% polypropylene fibres (PPF) and 2 or 4% steel fibres (StF), cured for 1, 28 (unsoaked), and 90 days (unsoaked, and soaked)
CBR (%)
100
unsoaked - 24 hrs unsoaked - 3 months
unsoaked - 28 days soaked - 3 months
75 50 25 0
t FP
F tF tF PP %S %S % 2 2 5 + + F C 0 .1 PP OP C+ % P 5 % O 30 0 .1 30% Pt+ C+ + F P t O FP 30% + t FP
PC %O 0 3 +
Figure 4.34: CBR values of different types of stabilized fibrous peat samples containing 30% cement with 0.15% polypropylene fibres (PPF), and 2% steel fibres(StF), cured for 1, 28 (unsoaked), and 90 days (unsoaked, and soaked)
149
Visual inspection of stabilized peat samples after each test indicated that, those samples that contained polypropylene fibres were more intact, and with fewer cracks than those samples without polypropylene fibres. Figure 4.35 shows comparison images of tested UCS stabilized peat samples between samples containing polypropylene fibres with samples not containing polypropylene fibres.
With PPF Without PPF
Figure 4.35: Degree of intactness in OPC treated UCS samples, with and without inclusion of polypropylene fibres
4.2.3d
Effect of ground granulated blast furnace slag (BFS) in strengthening OPC treated fibrous peat
Effects of BFS as an additive on stabilized fibrous peat with ordinary Portland cement have been examined, through UCS tests in this part of the study. Various trial mixtures of OPC treated with and without BFS were tested for their UCS values. Also, undisturbed, and samples made of only 5, 15, and 30% of OPC were tested as control measure samples as well. The stabilized samples were mixed initially with the fibrous peat’s natural moisture content (w = 200%) and air cured for three months. The results of various trial mixtures for UCS stabilized samples are shown in Figure 4.36. From these results, those samples which provided the highest strength values were chosen to conduct compaction test on their mixture types. OMC values obtained from compaction tests were then used to find CBR values of the chosen samples. 150
Four types of mixtures chosen for compaction test were fibrous peat with; a) 3.75% OPC, and 1.25% BFS b) 11.25% OPC, and 3.75% BFS c) 22.5% OPC, and 7.5% BFS d) 22.5% OPC, and 22.5% BFS Compaction tests results on the above samples are shown in Figure 4.37.
300 UCS (kPa)
250 200 150 100 50
un
di s. fib ro u
s FP pe T F at +2 Pt .5 FP +5 % % t+ O O PC PC FP 3.7 5 + t+ % 2 . O 3. PC 5% 75 BF +1 % S .2 BF 5% S BF + 1. S 2 FP FP 5 % t+ t+ OP FP 7. 15 C 5% t+ % 11 O O PC PC FP . 25 + % t+ 7. O 11 5% PC .2 BF 5% + 3 S . BF 75% S BF +3 .7 S FP FP 5% t+ t+ OP 30 C FP 15% % t+ O O 22 PC PC +1 FP . 5% 5 t+ O PC %B 22 FS .5 +7 % . 5 BF % BF S+ S 7. 5% OP C
0
Figure 4.36: Unconfined compressive strength for various types of stabilized fibrous samples with and without blast furnace slag
151
Figure 4.37: Dry density-moisture curves, for treated fibrous peat with different amount of ordinary Portland cement, and blast furnace slag CBR tests were conducted on four mentioned types of mixtures at the end of different curing periods. Curing periods used for the CBR samples were 24 hrs, 28 days, and 90 days. All the samples were tested under unsoaked condition. Also cured samples for 90 days not only were tested under unsoaked condition rather were tested under soaked condition as well. Figure 4.38 depicts the results of CBR tests.
152
120
CBR (%)
100 80
unsoaked - 24 hrs unsoaked - 3 months
unsoaked - 28 days soaked - 3 months
60 40 20 0
C C C C FS % O P FS FS FS OP OP OP B B B B % % % % % % 5 % 5 0 0 5 5 t+ 5 1 3 5 .5 2. Pt+ Pt+ Pt+ 3.7 FP 1.2 +7 +2 + F F F C C + C C P P P O O OP 5% O . 5% . 5% 5% 2 2 2 . 7 2 . t+ t +2 t+3 t +11 FP FP FP FP
Figure 4.38: CBR values of different types of stabilized fibrous peat samples treated with ordinary Portland cement, and blast furnace slag cured for 1, 28 (unsoaked), and 90 days (unsoaked, and soaked)
Results from Figure 4.36 indicate that, as the blast furnace slag contents of the stabilized samples are replaced by ordinary Portland cement, the UCS values decrease.
Test results on various types of stabilized fibrous peat samples shown in Figure 4.38 show that sample containing least OPC, and BFS gained the highest unsoaked CBR value (56.8%), and lowest when soaked (8.1%). This explains, as low contained OPC types of samples dry out through curing period, they gain strengths, and not because of their coherence, and intactness with binding agents (OPC, or BFS) due to chemical reactions, rather because of their fibre content. As the fibres of these types of stabilized samples lose their moisture contents, the stabilized samples become more solids and thus gain more strength, and as soon as they are soaked, their actual strengths reveal. Also, results from Figure 4.38, indicate that; generally samples stabilized with only OPC give better CBR results than
153
those samples which have blast furnace slag as additive. Also, as the curing period continues through 90 days, soaked CBR values continue to increase as well.
Some quantitative analyses obtained from Figures 4.36 include; a) The unsoaked UCS value of stabilized fibrous peat treated with 2.5% OPC and 2.5% blast furnace slag and cured for 90 days decreases by 19.6% (from 242 to 186 kPa), compared with peat treated with 5% OPC without the addition of blast furnace slag. b) The unsoaked UCS value of stabilized fibrous peat treated with 3.75% OPC and 1.25% blast furnace slag and cured for 90 days decreases by 0.8% (from 242 to 240 kPa), compared with peat treated with 5% OPC without the addition of blast furnace slag. c) The unsoaked UCS value of stabilized fibrous peat treated with 7.5% OPC and 7.5% blast furnace slag and cured for 90 days decreases by 17.3% (from 162 to 138 kPa), compared with peat treated with 15% OPC without the addition of blast furnace slag. d) The unsoaked UCS value of stabilized fibrous peat treated with 11.25% OPC and 3.75% blast furnace slag and cured for 90 days increases by 7.4% (from 162 to 174 kPa), compared with peat treated with 15% OPC without the addition of blast furnace slag. e) The unsoaked UCS value of stabilized fibrous peat treated with 11.25% blast furnace slag and 3.75% OPC treated and cured for 90 days decreases by 33.8% (from 162 to 121 kPa), compared with peat treated with 15% OPC without the addition of blast furnace slag. f) The unsoaked UCS value of stabilized fibrous peat treated with 15% OPC and 15% blast furnace slag and cured for 90 days decreases by 7% (from 240 to 224 kPa), compared with peat treated with 30% OPC without the addition of blast furnace slag. g) The unsoaked UCS value of stabilized fibrous peat treated with 22.5% OPC and 7.5% blast furnace slag and cured for 90 days increases by 0.8 % (from 240 to 242 kPa), compared with peat treated with 30% OPC without the addition of blast furnace slag. 154
Also some of the quantitative analyses obtained from Figure 4.38 regarding CBR values include; a) The unsoaked and soaked CBR values of stabilized fibrous peat treated with 3.75% OPC and 1.25% blast furnace slag and cured for 90 days increase by factors of over 71 (from 0.8 to 56.8%) and 10 (from 0.8 to 8.1%), respectively, compared with the CBR of undisturbed fibrous peat. b) The unsoaked and soaked CBR values of stabilized fibrous peat treated with 11.25% OPC and 3.75% blast furnace slag and cured for 90 days increase by factors of over 56 (from 0.8 to 45.2%) and 24 (from 0.8 to 19.5%), respectively, compared with the CBR of undisturbed fibrous peat. c) The unsoaked and soaked CBR values of stabilized fibrous peat treated with 22.5% OPC and 7.5% blast furnace slag and cured for 90 days increase by factors of over 61 (from 0.8 to 49%) and 27 (from 0.8 to 22.3 %), respectively, compared with the CBR of undisturbed fibrous peat. c) The unsoaked and soaked CBR values of stabilized fibrous peat treated with 22.5% OPC and 22.5% blast furnace slag and cured for 90 days increase by factors of over 65 (from 0.8 to 52.3%) and 40 (from 0.8 to 32.4%), respectively, compared with the CBR of undisturbed fibrous peat. d) As the curing period and the amount of OPC are increased in stabilized fibrous soils, their soaked CBR values also increase. 4.2.3e
Effect of fly ash (FA) in strengthening OPC treated fibrous peat
Effect of fly ash as an additive on stabilized fibrous peat with ordinary Portland cement, has been examined, through UCS tests in this part of the study as well. Various trial mixtures of OPC treated with and without fly ash were tested for their UCS values. Undisturbed, as well as 5, 15, and 30% of OPC samples with no additive were tested as control measure samples. The stabilized samples were mixed initially with the fibrous peat’s natural moisture content (w = 200%) and air cured for three months.
155
The results of trial mixtures for UCS stabilized samples are shown in Figure 4.39. From these results, those samples which provided the highest strength values were chosen to conduct compaction test on their mixture types. OMC values obtained from compaction tests were then used to find CBR values of the chosen samples.
Four types of mixtures chosen for compaction test were fibrous peat with: a) 2.5% OPC, and 2.5% FA b) 7.5% OPC, and 7.5% FA c) 15% OPC, and 15% FA d) 22.5% OPC, and 22.5% FA Compaction tests results on the above samples are shown in Figure 4.40.
300
UCS ( kPa)
250 200 150 100 50
un
di s. fib ro u
s pe FP at FP t+ t+ 2. 5 5% FP % O t+ O PC PC 3. 75 + 2. % FP 5% O t+ PC FA 3. +1 75 .2 % 5% FA FA +1 .2 5% FP FP O P t+ t+ C 7. 1 5% FP 5% t+ O O 11 PC PC .2 + 5% FP 7. 5% t+ O PC 11 FA .2 5% + 3. 75 FA % +3 FA .7 5% FP O FP P t+ C t+ 3 0 1 % 5% FP O t+ O PC 22 PC .5 + 15 % FP O % PC t+ FA 22 +7 .5 .5 % % FA FA +7 .5 % O PC
0
Figure 4.39: Unconfined compressive strength for various types of stabilized fibrous samples with and without fly ash
156
Figure 4.40: Dry density-moisture curves, for treated fibrous peat with different amount of ordinary Portland cement, and fly ash
CBR tests were conducted on four mentioned types of mixtures at the end of different curing periods. Curing periods used for the CBR samples were 24 hrs, 28 days, and 90 days. All the samples were tested under unsoaked condition. Also cured samples for 90 days not only were tested under unsoaked condition rather were tested under soaked condition as well. Figure 4.41 depicts the results of CBR tests.
157
120
unsoaked - 24 hrs unsoaked - 3 months
CBR (%)
100 80
unsoaked - 28 days soaked - 3 months
60 40 20
PC
FP t+ 50 %
O
PC
FP t+ 30 %
O
PC O
FP t+ 15 %
FP t+ 5%
O
PC
FA +2 2. 5% PC
FP t+ 22 .5 % O
O
PC
+1 5% FA
FA +7 .5 %
FP t+ 15 %
PC
FP t+ 7. 5% O
FP t+ 2. 5% O
PC
+2 .5 %
FA
0
Figure 4.41: CBR values of different types of stabilized fibrous peat samples treated with ordinary Portland cement, and fly ash cured for 1, 28 (unsoaked), and 90 days (unsoaked, and soaked)
Results from Figure 4.41 indicate that, all stabilized sample containing 50% OPC, and 50% fly ash give the highest values for UCS when a total of 5, 15, or 30% of ordinary Portland cement, as well as fly ash are used.
Based on the results obtained from Figure 4.39, the strength gain of low content ordinary Portland cement samples (2.5, and 5%) through air curing are not due to binding produced by calcium silicate hydrate (CSH) or the cementitious process that normally takes place as cement and water react. Also, their strength does not come from chemical bonds produced through cement, fly ash, and water, rather it is from the drying of the fibres within the peat samples. Thus, as the fibres lose their moisture content, they become more solid, and the samples gain strength. These samples containing low levels of OPC only gain strength when tested under unsoaked conditions, but they lose most of their gained strength values when tested under soaked conditions. CBR test results on these types of sample are 158
shown in Figure 4.42, and clearly shows soaked samples with low OPC dosage have much lower CBR values when compared with their respective unsoaked samples
Comparison of the results obtained from Figure 4.39, and 4.41, indicate that samples containing ordinary Portland cement provide more strength than samples containing OPC and fly ash. The reason for samples gaining more strength with OPC alone rather than OPC and fly ash may be explained by the fact that fly ash is a pozzolanic material and, when in contact with cement and water, calcium silicate hydrate is produced as gel. This gel surrounds each particle of fly ash and thus prevents it from early setting, and therefore causes the mix to set late (Axelesson et al. 2007; Janz and Johanson 2002). On the other hand, highly organic soils containing more than 75% organic materials such as peat contain a large amount of humic acid, which reacts with cement and produces insoluble products that make the stabilized peat set at retarded times, therefore when a pozzolanic material which can also be considered to be a retarder such as fly ash is added to the mixture of OPC and peat, this makes the mixture even more late setting. Thus it is possible to state that, when OPC alone is used to stabilize peat, it is expected to gain full strength through time and to be late setting and even more than three months that was used in this study. And when OPC is used along with fly ash to stabilize peat, the stabilization process may take even longer. Also, as the curing period continues through 90 days, soaked CBR values continue to increase as well. Some of the quantitative analyses of Figure 4.39 include; a) The unsoaked UCS value of stabilized fibrous peat treated with 2.5% OPC and 2.5% fly ash and cured for 90 days decreases by 14% (from 242 to 210 kPa), compared with 5% OPC without the addition of fly ash.
159
b) The unsoaked UCS value of stabilized fibrous peat treated with 3.75% OPC and 1.25% fly ash and cured for 90 days decreases by 15% (from 242 to 210 kPa), compared with 5% OPC without the addition of fly ash. c) The unsoaked UCS value of stabilized fibrous peat treated with 7.5% OPC and 7.5% fly ash and cured for 90 days decreases by 14% (from 162 to 140 kPa), compared with 15% OPC without the addition of fly ash. d) The unsoaked UCS value of stabilized fibrous peat treated with 11.25% OPC and 3.75% fly as and cured for 90 days decreases by 47% (from 162 to 110 kPa), compared with 15% OPC without the addition of fly ash. e) The unsoaked UCS value of stabilized fibrous peat treated with 15% OPC and 15% fly ash and cured for 90 days decreases by 18% (from 240 to 203 kPa), compared with 30% OPC without the addition of fly ash. f) The unsoaked UCS value of stabilized fibrous peat treated with 22.5% OPC and 22.5% fly ash and cured for 90 days decreases by 21% (from 240 to 198 kPa), compared with 30% OPC without the addition of fly ash. g) The highest UCS values after stabilized fibrous peat treated with only OPC are those for stabilized soils with a 50/50 ratio of OPC to fly ash.
Also some of the quantitative analyses regarding CBR values shown in Figure 4.41 include; a) The unsoaked and soaked CBR values of stabilized fibrous peat treated with 2.5% OPC and 2.5% fly ash and cured for 90 days increase by factors of over 46 (from 0.8 to 36.8%) and 6 (from 0.8 to 5%), respectively, compared with the CBR of undisturbed fibrous peat b) The unsoaked and soaked CBR values of stabilized fibrous peat treated with 7.5% OPC and 7.5% fly ash and cured for 90 days increase by factors of over 35 (from 0.8 to 28%) and 18 (from 0.8 to 14.9%), respectively, compared with the CBR of undisturbed fibrous peat 160
c) The unsoaked and soaked CBR values of stabilized fibrous peat treated with 15% OPC and 15% fly ash and cured for 90 days increase by factors of over 39 (from 0.8 to 31.7%) and 21 (from 0.8 to 17.1%), respectively, compared with the CBR of undisturbed fibrous peat. d) The unsoaked and soaked CBR values of stabilized fibrous peat treated with 22.5% OPC and 22.5% fly ash and cured for 90 days increase by factors of over 60 (from 0.8 to 48%) and 35 (from 0.8 to 28%), respectively, compared with the CBR of undisturbed fibrous peat. e) As the curing period and amount of OPC are increased in stabilized fibrous soils, their soaked CBR values also increase. f) More OPC used in the stabilization process gives more strength to the peat with a shorter curing period. g) Fibrous peat can be stabilized with mixtures of OPC and fly ash, but OPC alone provides higher CBR results in most cases
4.2.3.4
Linear shrinkages (LS)
Results of linear shrinkages for various types of stabilized peat that are shown in Figure 4.42 indicate that, as the OPC amounts are increased in samples, linear shrinkages decrease. Also as micro silica or polypropylene fibres are added to the stabilized samples, amounts of linear shrinkage decrease further.
With polypropylene fibres, due to the more connectivity of the particles by the fibre reinforcements linear shrinkages are reduced. For other types of samples decrease in linear shrinkage is due to amounts of their moisture contents and as the moisture contents decrease their linear shrinkages decrease as well.
161
Figure 4.42: Linear shrinkage for various types of stabilized fibrous peat with ordinary Portland cement, silica fume, and polypropylene fibre
4.2.3.5
Linear volume shrinkage indices (LVSI)
Because of the large surface area, dehydration as well as chemical reactions involved in stabilized peat during air curing, a significant volume change (shrinkage) occurs as a result of the change in moisture content. Linear volume shrinkage Index (LVSI) is an index parameter expressed in percentage (Equation 3.1) to represent the volumetric change of air cured stabilized peat.
Results of LVSI tests on various amounts of stabilized fibrous peat, with ordinary Portland cement (OPC), polypropylene fibres (PPF), silica fume (SFU), steel fibres (StF), blast furnace slag (BFS), and fly ash (FA) are shown in Figure 4.43 and Figure 4.44(a,b).
162
Figure 4.43: Linear volume shrinkage indices for various types of stabilized fibrous peat with ordinary Portland cement, silica fume a)
163
b)
Figure 4.44: Linear volume shrinkage indices for various types of stabilized fibrous peat with ordinary Portland cement, and different additives
Linear volume shrinkage index values for various types of stabilized fibrous peat obtained from Figure 4.44 indicate the following results; a) Plain fibrous peat has the highest LVSI of 36.19%. b) LVSI of stabilized fibrous peat with 15% OPC is 23.41%. c) Linear volume shrinkage indices of fibrous peat treated with 15% OPC and 0.15% polypropylene fibres or 10% silica fume is 11.28% and 14.29%, respectively. d) LVSI for stabilized fibrous peat containing 30% OPC and more is between 0 to 3%. e) As the amounts of OPC in the mixtures are increased, the LVSI decreases. f) The presence of various types of additive in the mixtures of peat and OPC decreases the LVSI values further.
164
4.2.3.6
Liquid limits and plastic limits
Results obtained from liquid limit (LL) values for various types of samples shown on Figure 4.45 indicate that, as the OPC contents of the stabilized samples increase, LL values decrease, also addition of silica fume and polypropylene fibres with the dosage rates shown in Figure 4.45, will decrease the LL values further. Effects of silica fume to decrease the LL values of the OPC treated samples are slightly more than polypropylene fibres.
Plastic limit (PL) tests results on all the samples that their LL values are shown in Figure 4.45 were conducted, and it was found none of them actually had a plastic limit.
Figure 4.45: Liquid limits for various types of samples
165
4.2.3.7
pH values
pH results for plain fibrous peat, and various types of samples treated with OPC and different additives are shown in Figure 4.46. 14 12 10
pH
8 6 4 2
Pa in
fib
ro u
s FP pe at t+ FP 5% t + OP 1 C FP 5% t + OP 3 C FP FP 0% t+ O t FP 5% +50 PC t + OP % 1 C O FP 0% + 1 PC t + OP 0 % 15 C S FP %O +1 0 FU PC % t+ S 3 FP 0% +1 0 FU t+ OP %S 5 C FP 0% +5 FU O t+ % P 5 C S FP %O +5 FU t+ PC % FP 10% + 1 S FU 0 t+ 15 OP %B % C+ F S FP O 5 t + PC %B 5% +1 FS FP O 5% t+ PC B FP 10% +1 FS 0 t+ 15 OP %F % C+ A O PC 5 % +1 FA 5% FA
0
Figure 4.46: pH values for various types of samples The results indicate that; a) As the plain fibrous peat is treated with different amount of OPC, its pH values increases. b) As the amount of OPC is increased, the pH for the samples increases further. c) Addition of silica fume (SFU) increases pH values of 5, and 15% OPC treated fibrous peat samples from 9.8 to 10.06 (for 5%), and also from 11.31 to 11.76 (for 15%). d) Addition of silica fume decreases the pH values of 30, and 50% OPC treated samples from 12.42 to 11.32 (for 30%), and from 12.78 to 11.93 (for 50%). e) Blast furnace slag and fly ash when added to OPC treated samples increase the pH values of the treated samples further.
166
4.2.4
Reinforcing fibrous peat with precast stabilized peat columns to increase load bearing capacity, and to reduce settlement of fibrous peat
Precast stabilized peat columns were used to reinforce plain peat in-order to increase peat load bearing capacity as well as to reduce its compressibility. These processes are explained with details in the following sections.
4.2.4.1
Shear strength parameters for precast stabilized fibrous peat columns
Consolidation undrained (CU) triaxial tests were conducted on various types of samples from undisturbed samples to stabilized samples with different types of precast columns. Table 4.2, shows the results of total, and effective stress shear strength parameters obtained from CU tests.
Table 4.2: Consolidated undrained shear strength parameter values for undisturbed fibrous peat, and different types of precast stabilized fibrous peat columns reinforcing undisturbed fibrous peat samples
167
In order to show the strength improvements of the stabilized fibrous peat samples with different types of precast columns, stress - strain curves were constructed for undisturbed and stabilized samples shown in Figure 4.47(a, b). Results shown in Figure 4.47 indicate that at some certain strains stabilized samples can carry more loads compared with undisturbed sample. a)
b)
Figure 4.47: Variation of deviator stress with axial strain in CU tests, a) Undisturbed, and stabilized samples with OPC with or without polypropylene fibres columns, b) Samples stabilized with OPC and additives (silica fume, blast furnace slag and fly ash) columns
168
Also from stress- strain curves shown in Figure 4.47 (a, and b), stress/ strain ratios at an arbitrary strain of 3.5% for various types of samples are presented in Figure 4.48. This Figure is more clear to show that the treated undisturbed fibrous peat samples with precast columns are effective to increases strength values of plain fibrous peat.
Figure 4.48: Stress/ strain ratios for untreated sample and reinforced samples with different types of precast columns
Results obtained from Table 4.2, as well as illustrative Figures 4.47, and 4.48 include; a) Precast stabilized peat columns improve the strength parameters of untreated fibrous peat b) Generally, as the OPC amounts of the columns increase, the strengths of the treated samples increase as well c) Polypropylene fibres and silica fume as additives when used in OPC treated columns improve the strength of the treated samples further d) Addition of polypropylene fibres seem to be more effective to increase the strength of treated columns compared with identical treated columns with silica fume
169
e) Addition of fly ash, or blast furnace slag to treated columns have caused the columns to have significant improvements in their strength values compared with other identical stabilized columns made of similar amounts of OPC, and polypropylene fibres or silica fume.
A reason that precast columns containing blast furnace slag or fly ash give better strength values than those obtained from three months old UCS or CBR samples may be explained by the fact that these two additives make the OPC treated samples to be late setting. In precast columns, the hardening process through chemical reactions and dehydration is much faster than samples being cured in normal temperature (as it was for UCS, and CBR samples), and they complete their hardening process in short time while being in high temperature upon drying.
4.2.4.2
Compressibility behaviour of fibrous peat reinforced with precast columns
Compressibility behaviours of fibrous peat have been examined through Rowe cell consolidation tests. This test has been conducted on various types of samples from undisturbed fibrous peat (as control measure sample) to undisturbed samples reinforced with various types of precast stabilized columns. The columns were made of fibrous peat, with ordinary Portland cement (OPC), with or without additives. Types of additives used for the stabilized columns were; polypropylene fibres (PPF), silica fume (SFU), blast furnace slag (BFS), as well as fly ash (FA).
In this study in order to evaluate the compressibility behaviour of samples reinforced with precast column, Rowe cell consolidation tests were conducted on undisturbed fibrous peat as well as undisturbed samples while reinforced with various types of precast stabilized fibrous peat columns. Modified compression index (Ccε), and recompression ratio (Crε) for each sample were computed based on Eqs. 2.4 and 2.5. The Ccε and Crε values for each type of stabilized sample were evaluated and
170
di s. fib ro u
s
pe FP at t+ 5% FP O PC t+ 15 FP %O PC t+ 30 % FP FP O t+ PC t+ 5% 5 0% FP O PC t+ O 15 PC +0 .1 FP %O 5 PC % t+ 30 PP + 0 % F .1 O PC 5% FP PP t+ + F 5% 0 .1 5% FP O PC t+ P 15 +1 PF % 0% O F SF PC FP Pt+ U +1 30 t+ 0% % 11 O .2 SF 5% PC U + 5% FP OP C t+ SF + 7. U 5 % 3.7 5% O PC B +7 FS .5 % FA
un
Recompression ratio di s. fib ro u
Modified compression index
s pe at FP t+ 5% FP O PC t+ 15 % FP O PC t+ 30 % FP FP O PC t+ t+ 5% 50 % FP O PC O t+ PC 15 +0 . % 1 FP 5% O PC t+ PP 30 +0 F % .1 O 5% PC FP PP +0 t+ F .1 5% 5% FP O PC PP t+ F 15 +1 % 0% O FP SF PC t+ U FP +1 3 t+ 0% 0% 11 O SF .2 5% PC U +5 O % FP PC SF t+ +3 U 7. .7 5% 5% O BF PC S +7 .5 % FA
un
presented in Figures 4.49 and 4.50. It is observed that the two indices decrease with an increase in the
OPC content.
0.3
0.25
0.2
0.15
0.1
0.05
0
Figure 4.49: Modified compression index (Ccε), values for undisturbed fibrous peat, and samples stabilized with various types of columns
0.04 0.035 0.03 0.025 0.02 0.015 0.01 0.005 0
Figure 4.50: Recompression ratio (Crε), values for undisturbed fibrous peat, and samples stabilized with various types of columns
171
Some of the quantitative analyses obtained from Figures 4.49, and 4.50 include; a) Modified compression index reduced from 0.269 for undisturbed fibrous peat to 0.105 for peat stabilized with 50% OPC (reduced by factor of over 20). b) A column treated with 30% OPC reduces the Ccε and Crε of plain fibrous peat by factors of over 2 (from 0.269 to 0.111) and over 4 (from 0.0362 to 0.0081), respectively. c) A column with 30% OPC and 0.15% polypropylene fibres reduces the Ccε and Crε of plain fibrous peat by factors of 3 (from 0.269 to 0.104) and 4 (from 0.0362 to 0.009). d) A column with 30% OPC, 0.15% polypropylene fibres and 5% silica fume reduces the Ccε and Crε of plain fibrous peat by factors of 3 (from 0.269 to 0.105), and 4 (from 0.0362 to 0.0086). e) A column treated with 11.25% OPC and 3.75% blast furnace slag reduces the Ccε and Crε of plain fibrous peat by 38.7% (from 0.269 to 0.194) and a factor of 2 (from 0.0362 to 0.0190) respectively f) A column treated with 7.5% OPC and 7.5% fly ash reduces the Ccε and Crε of plain fibrous peat by factors of 2 (from 0.269 to 0.134), and 4 (from 0.0362 to 0.0092) respectively g) As the amount of OPC is increased in precast columns, the Ccε and Crε values continue to decrease compared with the original values for unreinforced fibrous peat. The inclusion of polypropylene fibres or silica fume further reduces the Ccε and Crε values
It is apparent from the results that the Ccε can be reduced to a large extent with the use of ordinary Portland cement and polypropylene fibres, and silica fume. Blast furnace slag, when used in precast columns Ccε, and Crε values decrease by 39% (from 0.269 to 0.1941), and 91% (from 0.362 to 0.0190) respectively. On the other hand when fly ash is used as an additive to OPC treated precast peat columns reduces Ccε, and Crε values by over 101% (from 0.269 to 0.1336), and 291%(from 0.036 to 0.0092) respectively compared with the unreinforced fibrous peat.
172
In general, based on the results obtained from Figures 4.49, and 4.50, undisturbed fibrous peat when reinforced with precast stabilized columns, their modified compression indices, as well as their recompression ratios drop. Also, use of additives in OPC treated precast columns reduce modified compression indices, as well as recompression ratio values further. Modified compression indices for precast columns containing 15% OPC, 15% OPC with 0.15% polypropylene fibres, 15% OPC with 10% silica fume, 7.5% OPC with 7.5% fly ash, and 11.25% OPC with 3.75% blast furnace slag show that Ccε drops by 124, 134, 130, 101, and 38.5% respectively, compared with the unreinforced (undisturbed) fibrous peat.
Also recompression ratios for the same type of samples mentioned for modified compression indices show that Crε reduce by factors of; 2.9, 2.94, 2.94, 3.91, and 1.91 respectively, compared with the unreinforced (undisturbed) fibrous peat.
Addition of silica fume increases the recompression ratios slightly, as compared with the Crε of those samples with peat and ordinary Portland cement only. The percentage increases in Crε with 5, 15 and 30% OPC are 23% (from 0.0161 to 0.0198), 0.6% (from 0.0122 to 0.0123), and 6 % (from 0.0081 to 0.0086).
Also, the reduced values of Ccε and Crε can be attributed to the fact that the OPC reacts with water to form calcium silicate hydrate and calcium hydroxide in columns. Silica fume reacts with the calcium hydroxide in presence of water to form calcium silicate hydrate. The increase in strength is a result of the increased calcium silicate hydrate gel in the cement paste, chemical reactions, and dehydrations of the precast stabilized peat columns reinforcing fibrous peat. Also in fibre reinforced precast columns the fibre surface is attached by many soil particles which make the contribution to bond strength and friction between the fibre and soil matrix. The distributed discrete
173
fibres act as a spatial three dimensional network to interlock soil grains, help grains to form a unitary coherent matrix and restrict the displacement. Consequently, the stretching resistance between peat particles and strength behaviour is improved (Tang et al. (2007).
Fly ash is a pozzolanic material and need activator throughout its reaction such as Ca(OH)2, when in contact with cement and water. From the reaction calcium silicate hydrate is produced as gel, this gel surrounds each fly ash particle, and prevents it from early setting (Janz 2002; Axelsson et al. 2002). This is probably the reason, that fly ash when used as an additive to stabilized OPC treated peat samples has given better results when used in precast columns than those stabilized samples in normal air temperature (UCS, and CBR samples). Drying the columns probably has caused the pozzolanic reactions to take place in a faster rate, and thus giving more strength to the precast columns.
4.2.4.3
Load bearing capacity
In order to evaluate the bearing capacity of fibrous peat stabilized by precast columns, load bearing capacity test was carried out in the test tank. For carrying out load bearing capacity test, the tank was remoulded with fibrous peat up to a depth of 1.0 m. A total of seven load bearing capacity tests were conducted with each test having the following descriptions: i)
Remoulded fibrous peat having the same bulk density as in the field (plain or untreated fibrous peat)
ii)
Remoulded fibrous peat reinforced with precast column (D = 200 mm, and L = 1000 mm) made of fibrous peat and 15% ordinary Portland cement (OPC)
iii)
Remoulded fibrous peat reinforced with precast column (D = 200 mm, and L = 1000 mm) made of fibrous peat, 15% OPC and 10% silica fume (SFU)
174
iv)
Remoulded fibrous peat reinforced with precast column (D = 200 mm, and L = 1000 mm) made of fibrous peat and 20% OPC
v)
Remoulded fibrous peat reinforced with precast column (D = 200 mm, and L = 1000 mm) made of fibrous peat, 15% OPC and 0.15% polypropylene fibres (PPF)
vi)
Remoulded fibrous peat reinforced with precast column (D = 200 mm, and L = 1000 mm) made of fibrous peat, 0.15% OPC, 15%PPF, and 2% steel fibres (StF)
vii)
Remoulded fibrous peat reinforced with precast column (D = 300 mm, and L = 1000 mm) made of fibrous peat and 15% OPC
The load deformation curves for various types of samples mentioned above are shown in Figure 4.51. Load (kN) 0
2
4
6
8
10
12
14
16
18
20
22
0
Deformation (mm)
20 40 60 80 100 120 140 160
Plain FPeat FPt+15 %OPC
FPt+15% OPC+SFU
FPt+20 %OPC
FPt+15 %OPC +PPF
FPt+15 %OPC+ PPF+StF
FPt+15% OPC (300 m m dia.)
Figure 4.51: Load – deformation curves From load deformation curves, it is observed that in the case of fibrous peat only, there is a punching failure and as the load intensifies, the deformations increase with a constant rate. Since, the failure point from the load – deformation curve for the plain fibrous peat is not detectable and as the load increases the plate plunges in to the peat inside the test tank further, therefore the failure load for this 175
particular situation is assumed to be at 10% of the plate load diameter or 60 mm. Failure loads for other types of samples are where there is a large deformation occurring due to extra applied loads during the testing procedures, and they can be easily detected from the curves shown in Figure 4.51.
Comparing the load at failures from curves shown in Figure 4.51, the load bearing capacity of the fibrous peat increase from 3.2 kN to following values when reinforced with various types of columns; a) For 200 mm diameter stabilized column treated with 15% OPC, the LBC increases to 7 kN, an increase of 118% (from 3.2 kN). b) For 200 mm diameter stabilized column treated with 15% OPC and 10% silica fume, the LBC increases to 10.3 kN, an increase of more than 221% c) For a 200 mm diameter column treated with 20% OPC, the LBC increases to 11.5 kN, an increase of 260% d) For a 200 mm diameter column treated with 15% OPC and 0.15% polypropylene fibres, the LBC increases to 13.3 kN, an increase of more than 315% e) For a 200 mm diameter column treated with 15% OPC, 0.15% polypropylene fibres and 2% steel fibres, LBC increases to 18.3 kN, an increase of more than 471% f) For a 300 mm diameter stabilized column treated with 15% OPC, the LBC increases to 19.3 kN, an increase of 503%
Also, load deformation curves show that polypropylene fibres is more effective than silica fume, and when steel fibres with dosage rate of only 2% is used along with 0.15% polypropylene fibres, the load bearing capacity of the column increases significantly. Also as OPC amount or diameter of the columns are increased, the load bearing capacity of the columns increase as well. Shapes of the curves at close to the failure loads indicate that, columns having polypropylene fibres seem to be less brittle compared with other types of precast columns. 176
Load bearing capacity tests confirmed the following results obtained from CU, and Rowe cell tests for fibrous peat reinforced with precast stabilized peat columns; a) As the amount of ordinary Portland cement is increased in the precast columns, the load bearing capacity of the reinforced fibrous peat also increases b) As the diameter for the columns increases, the load bearing capacity of the reinforced fibrous peat also increases c) The inclusion of additives (polypropylene fibres, silica fume, and the use of polypropylene and steel fibres in combination) in precast columns treated with OPC increases the load bearing capacity of the reinforced fibrous peat further
From loading, and unloading curves shown in Figure 4.52, it is possible to observe the extent of rebounds for unreinforced fibrous peat to be 10.9 mm (from 96.3 to 80.2), and for when fibrous peat is reinforced with precast column to be16.1 mm (from 87.85 to 76.95). This result indicates that, fibrous peat when reinforced with columns, its behaviour tends to be more elastic than plastic.
0
0.5
1
Load (kN)
1.5
2
2.5
Deformation (mm)
0 20 40 60
loading unloading
80 100 120
plain fibrous peat
FPt+15%OPC(300 mm dia. column)
Figure 4.52: Loading and unloading for plain fibrous peat and fibrous peat reinforced with OPC treated 300 mm precast column 177
4.2.4.4
Finite element method (FEM)
Finite element analysis was carried out on three selected type of samples. The objective of FEM analysis was to verify the settlements amount at failure loads obtained from actual tests, and also to observe the behaviour of stress distribution in selected samples at failure. Three types of sampler used for FEM analysis are; i)
Plain fibrous peat (unreinforced)
ii)
Fibrous peat reinforced with 15% OPC treated, 200 mm diameter column
iii)
Fibrous peat reinforced with 15% OPC treated, 300 mm diameter column
PLAXIS soft ware program was used for the analysis. Computer simulations for each type of sample were similar to the actual tests conditions. The main parameters that were used for each type of sample are shown in Table 4.3. Values shown in this Table are found from actual tests, except those which are marked with (*) that were assumed.
Table 4.3: Main parameters used for FEM analysis
* Assumed values Finite element analysis, for the three selected samples described above in load bearing capacity tests showed close agreement between the simulated and the experimental deformation values (Figure 4.53). 178
Figure 4.53: Comparison of deformation values found from actual load bearing tests and FEM analysis for three types of tested samples
The results of the finite element analysis in the form of effective principal stress diagrams are also presented in Figure 4.54. It is observed that the effective principal stress is 12.03 kN/m2 for plain (unreinforced) fibrous peat (Figure 4.54a). It increases significantly to 98.41 kN/m2 when 15% OPC treated precast column with 200 mm diameter is used as reinforcement for fibrous peat (Figure 4.54b). This shows the reason fibrous peat when stabilized with precast column can take higher load because of increased stiffness of the column. When the same amount of OPC (15%) is used to make the column and only the diameter is increased from 200 mm to 300 mm, the effective principal stress further increases to 183.84 kN/m2, leading to a still higher load carrying capacity (Figure 4.54).
179
a)
b)
c)
Figure 4.54: Effective principal stress diagrams, (a) Plain fibrous peat, (b) Fibrous peat reinforced with 15% OPC treated 200 mm diameter column and (c) Fibrous peat reinforced with 15% OPC treated 300 mm diameter column
4.2.4.5
Index properties for hemic, and sapric peats
Hemic, and sapric peat samples, were tested for some of their more significant index properties before being used as precast columns and tested for consolidated undrained triaxial, as well as Rowe cell consolidation tests. Particle size distribution curves for hemic, peat is shown in Figure 4.55. Also, Table 4.4 shows some index properties for hemic and sapric peats.
180
Figures 4.55: Particle size distribution for hemic peat
Table 4.4: Index properties of hemic and sapric peats
According to the results shown on Table 4.4, as the particle size of the peat samples become finer, they tends to be less organic. This is probably due to more fine clay particles contents in sapric peat which makes this type of peat to be less organic compared with hemic or fibric peats. Results from obtained pH values for each type of peat also indicate that sapric peat used in the study is less acidic than the hemic peat. SEM test results for hemic and sapric peat shown in Figure 4.56 shows the degree of particles fineness of sapric peat compared with hemic peat and confirms the sieve analysis result for the hemic peat shown in Figure 4.55 as well.
181
a)
b)
Figure 4.56: SEM for a) sapric, and b) hemic peats
4.2.4.6
Shear strength parameters for precast stabilized hemic and sapric peat columns
Precast stabilized hemic, and sapric peat columns were prepared as were prepared for precast columns made of fibrous peat explained earlier. Undisturbed fibrous peat samples were reinforced with hemic, or sapric precast stabilized columns, and then shear strength parameters of each type of sample was evaluated through CU tests. Table 4.5 shows results for CU triaxial tests conducted on samples made of 15% OPC treated hemic or sapric peats with and without 0.15% polypropylene fibres. Table 4.5: Consolidated undrained shear strength parameter values for different types of precast stabilized hemic or sapric columns reinforcing undisturbed fibrous peat samples
182
Figure 4.57 and Figure 4.58 show the variations of stress - strain, as well as strain/stress ratio obtained from CU triaxial tests respectively. The results indicate that OPC treated columns made from hemic and sapric peats improve the strength of unreinforced fibrous peat. Polypropylene fibres (PPF) when added to the mixtures increase the strengths further.
Figure 4.57: Variation of deviator stress with axial strain in CU tests for various types of samples Also from stress - strain curves shown in Figure 4.57, stress/ strain ratios at an arbitrary strain of 3.5% for various types of samples are presented in Figure 4.58. This Figure is more clear to show that the treated undisturbed fibrous peat samples with precast columns made of sapric and hemic peats are also effective to increases strength values of plain fibrous peat, and polypropylene fibres when used as additive adds further strength to the stabilized columns as well.
183
Figure 4.58: Stress – Strain ratios for various types of samples
4.2.4.7
Compressibility behaviour of fibrous peat reinforced with OPC treated sapric precast columns
Compressibility behaviours of precast stabilized peat (hemic, or sapric peat) have been investigated through Rowe cell consolidation tests. Two consolidation parameters, Modified compression index (Ccε), and compression ratio (Crε) for each sample were computed using Equations 2.4, and 2.5. Undisturbed fibrous peat samples have been reinforced with precast stabilized hemic or sapric peats, and their Ccε and Crε have been evaluated. Binding agent used in this part of the study was also ordinary Portland cement. Two types of additives; polypropylene fibres (PPF) and silica fume (SFU) were used to make precast stabilized columns as well.
Sample and column preparations for Rowe cell consolidation tests were identical to those described earlier for columns made of fibrous peat columns. Results of modified compression indices, and
184
compression ratios for various types of materials found from Rowe cell consolidation tests are shown in Figure 4.59.
Figure 4.59: Modified compression index, and recompression ratio (Ccε and Crε) values for various types of samples
Results obtained from Figure 4.59 shows that; a) A precast column made from sapric peat treated with 15% OPC causes reductions in Ccε and Crε of 117% (from 0.269 to 0.124) and 95% (from 0.0362 to 0.0186), respectively, when reinforcing plain fibrous peat b) A pre-cast column made from sapric peat treated with 15% OPC and 0.15% polypropylene fibres causes reductions in Ccε and Crε of 189% (from 0.269 to 0.100) and 229% (from 0.0362 to 0.0110), respectively, when reinforcing plain fibrous peat c) A precast column made from sapric peat treated with 15% OPC and 10% silica fume causes reductions in Ccε and Crε of 169% (from 0.269 to 0.10), and 229% (from 0.0362 to 0.011), respectively, when reinforcing plain fibrous peat 185
d) A precast column made from hemic peat treated with 15% OPC and 0.15% polypropylene fibres causes reductions in Ccε and Crε of 153% (from 0.269 to 0.1063) and 307% (from 0.0362 to 0.0089), respectively, when reinforcing plain fibrous peat e) A precast column made from hemic peat treated with 15% OPC and 10% silica fume causes reductions in Ccε and Crε of 149% (from 0.269 to 0.108) and 194% (from 0.0362 to 0.0123), respectively, when reinforcing plain fibrous peat
4.3
Liquid limits for stabilized hemic and sapric peats
Figure 4.60 shows that addition of silica fume to the peat samples (hemic or sapric) reduces the liquid limits of the samples further when compared with samples containing polypropylene fibres. This is possibly due to the presence of fibres in the mixtures, rather than any type of chemical reactions. 160 140 Liquid limit (%)
120 100 80 60 40 20 0 hemic peat + hemic peat + 15% C + 0.15% 15% C + 10% PF SFU
sapric peat + sapric peat + sapric peat + 15% C 15% C + 0.15% 15% C + 10% PPF SFU
Figure 4.60: Liquid limits for different types of stabilized samples
186
4.4
Comparison of various techniques to stabilize fibrous peat
In this section, a comparison discussion regarding past results obtained from other researchers with the obtained results from this study based on strength evaluation, material cost, and ease of field applicability for different techniques used to stabilize fibrous peat is being presented. Results are tabulated, with each Table presenting results for various methods used for stabilization of fibrous peat.
Table 4.6, shows the notations used in the following Tables (4.7, and 4.8) to clarify their contents. Table 4.7a, compares strength values, materials costs, and also designates a level of field applicability (from easiest to hardest) for each method used by various researchers to stabilize fibrous peat. In easiest designated level, least work is to be done in order to reach to the desired obtained results, and this implies to moist curing technique that requires no extra effort after mixing and compaction process. On the other hand moist curing with surcharge load of 100 kPa is the hardest process, since applying surcharge load during the curing process needs lots of extra efforts (loading the area, as well unloading process) , and as the amounts of surcharge loads are increased the amounts of works to be done are increased as well. Air curing method used in current study is designated with “relatively easy” level of difficulty in relation to its applicability in field, and that is because this process can be achieved at field by keeping the ground water level below the treated depth of peat which is not considered very difficult. This process can be done easily by pumping the water out during the curing process from the stabilization area.
Table 4.7b presents the obtained results of the current study to express the same parameters presented in Table 4.7a. Thus, Table 4.7a, and 4.7b can be used to compare the advantages or possible disadvantages of various techniques used to stabilize fibrous peat. The obtained results relating current study has been tabulated only for when 15% OPC is used to stabilize fibrous peat. 187
Table 4.8, compares various parameters obtained from other researchers relating different types of columns reinforcing fibrous peat with the results obtained from current study. Also, Table 4.9 presents the obtained results of unsoaked and soaked CBR values obtained from various types stabilized fibrous peat using OMC values obtained from moisture – density curves, and air cured up to 90 days.
Table 4.6: Definitions of various notations used in Tables 4.7 a, and 4.7b Notation
3 5 6 7 A B C D G RCT PLT PCC Co.In (Cc)
Description Curing period (day) Amount (kg/m3) Cost (RM/m3) Curing type Moist curing Moist curing with 10 kPa surcharge load Moist curing with 18 kPa surcharge load Moist curing with 100 kPa surcharge load Air curing Rowe cell consolidation test Plate load test Precast stabilized peat columns Compression index
188
Table 4.7a: Comparison of strength values, material costs, and ease of field applicability for various methods proposed by past researchers to stabilize fibrous peat
TEST RESEAR CHERS
Type
Value
3 , 7
(Unit) Axelsson et.al (2002) Axelsson et.al (2002) Axelsson et.al (2002) Hebib & Farrel l (2003) Hebib & Farrel l (2003) Hebib & Farrel l (2003) Hebib & Farrel l (2003) Hebib & Farrel l (2003) Alwi (2007) Alwi (2007) Alwi (2007) Alwi (2007) Wong et .al (2008b)
OPC
ADDITIVES Blast
5,6
UCS (Su)
80 (kPa)
28, C
150, 35
UCS (Su)
325 (kpa)
28, C
125, 29
UCS (Su)
175 (kPa)
28, C
125, 29
UCS (Su)
210 (kPa)
28, C
150, 35
UCS (Su)
70 (kPa)
28, C
90, 21
UCS (Su)
40 (kPa)
28, C
120, 28
UCS (Su)
30 (kPa)
28, C
UCS (Su)
17 (kPa)
28, C
30, 7
UCS (qu) UCS (qu) UCS (qu) UCS (qu) UCS (qu)
156 (kPa) 130 (kPa) 60 (kPa) 315 (kPa) 195 (kPa)
56, B 56, B 7, B 7, B 7, D
200, 46 125, 29 170, 39 213, 49 255, 59
Furna ce
Slag
5,6
125 , 19
60 , 14
15 , 35
Fly Ash
5,6
Sodium
Bento nite
5,6
TOTAL
COST Sand
FIELD
APPLICABILTY
(Level of Easiness)
(RM/m3)
5,6
125 , 19
30 , 5
130 , 20 125, 163 30, 39 38, 49 45, 59
189
FILL ER
280, 17 656, 40 800, 48
35
Relatively hard
58
Relatively hard
48
Relatively hard
35
Relatively hard
35
Relatively hard
33
Relatively hard
35
Relatively hard
27
Relatively hard
46
Hard
192
Hard
95
Hard
137
Hard
166
Hardest
Table 4.7a Continuing.....
Wong et .al (2008b) Wong et .al (2008b) Hashim, Islam (2008a)
UCS (qu)
100 (kPa)
7, D
225, 52
UCS (qu)
12 (kPa)
7, D
225, 52
UCS (qu)
43 (kPa)
28, A
298, 68
75 , 17 75 , 17
53, 69
800, 48
117
Hardest
400, 24
93
Hardest
400, 24
161
Easiest
Table 4.7b: Comparison of strength values, material costs, and ease of field applicability levels used in current study to stabilize fibrous peat
TEST
Types UCS , CBR UCS, CBR UCS, CBR UCS, CBR* UCS†, CBR* UCS†, CBR*
Values (Units)
OPC
3 , 7
5,6
96, (kPa) 7(%) 110, (kPa) 15(%) 165, (kPa) 16 173, (kPa) 22(%) 174, (kPa)
90, 155, G 36
174, (kPa)
90, G
20(%)
15(%)
ADDITIVES
TOTAL
PP Fibres
Silica Fume
Steel Fibr es
Blast Furnace Slag
Fly Ash
5,6
5,6
5,6
5,6
5,6
90, 155, 1.55, G 36 5 90, 155, G 36 90, 200, G 46
15.5, 12 2.4, 7
30, 17
90, 210, G 48
53,12
78, 18
78, 12
* Mixture at OMC †Unsoaked values
190
FIELD
COST
APPLICABILTY
(RM/m3)
(Level of Easiness)
36
Relatively easy
41
Relatively easy
48
Relatively easy
70
Relatively easy
60
Relatively easy
30
Relatively easy
Results obtained shown on Table 4.7a from past researchers indicate that fibrous peat may be stabilized to various degrees of success depending on several factors such as each method’s achieved strength, total cost, and the degree of easiness when applied to the field. Among the various proposed techniques to stabilize fibrous peat shown in Table 4.7a, one method falls in to the easiest degree of field applicability, which is defined earlier in this section or when moist curing technique is used. Even this method is easy to be applied at field to stabilize fibrous peat, using this method has several disadvantages as well. The disadvantages for moist curing include; lower obtained strength values, and higher total cost compared with others.
Also, Table 4.7b depicts the results obtained from air curing techniques used in this study to cure the OPC treated fibrous peat. Air curing technique is designated as one of the relatively easy method to cure stabilize peat, since this technique involves pumping the water out of the treated area to below the stabilized depth, and keeping it lowered to the same level during the curing period. The strength values, as well as total costs presented in Table 4.7b indicate that, air curing may be used to treat fibrous peat with relatively higher efficiency that includes high strength values as well as lower total cost compared with other techniques used by past researchers shown in Table 4.7a.
Various types of columns to stabilize peat used by other researchers, as well as precast stabilized peat columns used in this study are also compared in a tabulated form, and presented in Table 4.8. This comparison is based on several factors including; a) Type of tests performed b) Test’s results c) Curing periods, and types d) Type of admixtures used for stabilization e) Amounts of admixtures 191
f) Cost of admixtures g) Field applicability Table 4.8: Comparison of strength values, material costs, and ease of field applicability levels using various types of columns proposed by various researchers to stabilize fibrous peat TEST RESEA RCHER S Black et.al (2007) Black et.al (2007) Hebib & farrel (2003) Duraisam y et.al(2007, 2009) Kazemian , Huat (2009)
Current study
Current study
Current study
Type (unit)
PLT Load
Value
7
Increas e by
_
(kN)
50%
PLT
Increas e by
Load
(kN) PLT
Settl. (mm)
RCT Co.In
(Cc) RCT Co.In
Co.In
_
88%
Reduce by
28 , C
Reduce by
28 , A
Reduce by
28 , A
Reduce by
P CC
97%
50%
26%
(Cc) RCT
3 ,
55%
(Cc)
RCT Co.In
Reduce by
57%
P CC
(Cc)
RCT Co.In
(Cc)
Reduce by
57%
P CC
ADDITIVES
FIL LE R
TOTAL COST
Sand
(RM/m3)
(Level of Easiness)
60
Easiest
N/A
Relatively hard
225 , 52
56
Relatively hard
1350
311
Easiest
309 , 71
71
Relatively easy
OPC
5,6
PP Fib.
5,6
S. Fum
5,6
B.F Slag
5,6
F. Ash
5,6
5,6 60
No cement used, only a stainless caged steel filled with granular material was used in a columnar form
190 , 44
200 , 46
190 , 44
44
FIELD
APPLICABILTY
Relatively easy (If Mass produced)
1.9 , 6
52
Relatively easy (If Mass produced)
19 , 14
192
58
Relatively easy (If Mass produced)
Table 4.8 Continuing..........
Current study
Current study
Current study
Current study
Current study
Current study
RCT Co.In
Reduce by
28%
P CC
(Cc)
RCT Co.In
Reduce by
43%
P CC
(Cc)
PLT
Load
(kN)
PLT
Load
(kN)
PLT
Load
(kN)
PLT
Load
(kN)
Increas e by
118%
Increas e by
221%
Increas e by
260%
Increas e by
471%
P CC
P CC
P CC
P CC
210 , 48
53 , 12
60
(If Mass produced)
83 , 19
83 , 13
190 , 44
32
Relatively easy (If Mass produced)
44
Relatively easy (If Mass produced)
190 , 44
19 , 14
58
Relatively easy (If Mass produced)
200 , 46
200 , 46
Relatively easy
46
Relatively easy (If Mass produced)
+ (Steel fibres)
2.4 , 7
30 , 17
70
Relatively easy (If Mass produced)
From the results presented in Table 4.8, it is possible to observe that precast stabilized peat columns made of 15% OPC, 0.15% polypropylene fibres, and 2% steel fibres increase the load bearing capacity of untreated fibrous peat substantially and up to 471%, with relatively low price of 70 RM/m3 compared with methods used by other researchers shown in the same Table to stabilize (reinforce) fibrous peat.
193
Production of precast stabilized peat columns in Table 4.8 has been assumed to be relatively easy. This assumption is based on consideration that, the idea of this type of columns is new, and thus, mass production of the columns may be compared with producing precast concrete sections that are made outside the construction sites and then delivered to the construction sites prior to be used.
Table 4.9: Results for obtained CBR values using optimum moisture contents Use of optimum moisture contents
Curing period for CBR tests 1 28 Unsoaked Soaked day day (90 days) (90 days)
Type of stabilized fibrous peat Plain fibrous peat Fib. Pt + 5% OPC Fib. Pt + 10% OPC Fib. Pt + 15% OPC Fib. Pt + 20% OPC Fib. Pt + 30% OPC Fib. Pt + 50% OPC Plain fibrous peat + 0.15% pp fibres Fib. Pt + 5% OPC + 0.15% pp fibres Fib. Pt + 10% OPC + 0.15% pp fibres Fib. Pt + 15% OPC + 0.15% pp fibres Fib. Pt + 20% OPC + 0.15% pp fibres Fib. Pt + 30% OPC + 0.15% pp fibres Fib. Pt + 50% OPC + 0.15% pp fibres Fib. Pt + 5% OPC + 10% silica fume Fib. Pt + 10% OPC + 10% silica fume Fib. Pt + 15% OPC + 10% silica fume Fib. Pt + 30% OPC + 5% silica fume Fib. Pt + 5% OPC + 2% steel fibres + 0.15% pp fibres Fib. Pt + 5% OPC + 4% steel fibres Fib. Pt + 5% OPC + 4% steel fibres + 0.15% pp fibres Fib. Pt + 15% OPC + 2% steel fibres + 0.15% pp fibres Fib. Pt + 15% OPC + 4% steel fibres Fib. Pt + 15% OPC + 4% steel fibres + 0.15% pp fibres Fib. Pt + 30% OPC + 2% steel fibres Fib. Pt + 30% OPC + 2% steel fibres + 0.15 pp fibres Fib Pt + 3.75% OPC + 1.25% Blast furnace slag Fib. Pt + 11.25% OPC + 3.75 % Blast furnace slag
194
2.5 7.4 9.4 12.6 14.5 18.5 36.7 0.5 2.8 10.4 12.5 14.8 17.2 33.6 6.6 11.1 12.1 14.4 4.7
8.2 19.2 23.8 34 40.4 54.8 74.6 9.3 13.6 26.3 30.4 35.2 36.7 65 19.9 25.5 38.4 43.5 14
32.6 53.3 55 60.4 66.3 71 115 44.3 61 57 63.5 77 91.9 145 76 65.2 68.4 88.6 67.8
1.4 2.3 15.2 22 32 40.2 110 4 13.45 23.1 28.2 38.7 48.5 141 4.6 16 24.2 43.8 15.5
9.5 7.8
15.5 16.8
56.7 72.8
13.7 17
21.5
44
75
33.3
28.3 22.1
48.2 51.2
70 78
34.6 40.4
30.5 38.8
58 67
72.8 99.8
43.6 55.4
5.8 9.2
19 27.6
56.8 45.2
8.1 19.5
Fib. Pt + 22.5% OPC + 7.5% Blast furnace slag Fib. Pt + 22.5% OPC + 22.5% Blast furnace slag Fib. Pt + 2.5% OPC + 2.5% Flay ash Fib. Pt + 7.5% OPC + 7.5% Fly ash Fib. Pt + 15% OPC + 15% Fly ash Fib. Pt + 22.5% OPC + 22.5% Fly ash
12 13 6.1 13 11.8 16.8
Table 4.9 continuing…….
34 38.5 19 16 28.8 34.5
49 52.3 36.8 28 31.7 48
22.3 32.4 5 14.9 17.1 28
Also Table 4.9 compares CBR values obtained for various types of stabilized mixtures used in this study. All the values shown in this Table were achieved using each mixture’s optimum moisture content from moisture – density curves. General trend of improvements, for CBR values shown in this Table indicates that, as the cement amount increases, the soaked CBR values tend to increase as well. Polypropylene fibres, silica fume, and steel fibres when added to each mixture, increase the CBR values further, while blast furnace slag, and fly ash when used as additives to OPC treated fibrous peat can stabilize untreated peat, but their involvements are not as effective as when OPC alone is used to stabilize fibrous peat.
4.5
Reproducibility of samples
Since, air curing technique of preparing the stabilized samples is still in its nascent stage of development, tests were carried out to determine the repeatability of sample preparation. The stressstrain curves for UCS of four samples (ordinary Portland cement, 15%, air cured for 300 days) are presented in Figure 4.61.
It was observed from the strain-strain curves that the peak stress at failure are 412.02, 422.00, 446.09 and 469.1 at strains varying from 5 - 7%. The mean value of the four samples is 437.30 and the standard deviation is 25.57.
195
Confidence limits are expressed in terms of a confidence coefficient. Although the choice of confidence coefficient is somewhat arbitrary, in practice 90%, 95%, and 99% intervals are often used. The confidence level tells, how sure the results actually are. For any scientific study, one where the results really matter, most researchers use the 90, or 95% confidence level, or at least start at this level and then try to rise higher
For this study, the 90% confidence interval is (407.21, 467.39) and the 95% confidenece interval is (396.61, 477.99). Hence, it can be said that the results are very close to a resonable confidence level of 90%. sample 1
sample 2
sample 3
sample 4
500
Stress (kPa)
400 300 200 100 0 0
1
2
3
4
5
6
7
Strain (%)
Figure 4.61: Reproducibility samples for UCS tests
196
8
9
CHAPTER 5
CONCLUSIONS AND RECOMMENDATIONS
5.1
Conclusions
One of the most troublesome of soft and highly organic soils with more than 75% organic materials is fibrous peat, due mainly to their high compressibility and low shear strength.
Shallow and deep stabilizations have been studied to improve strength as well as to reduce compressibility of fibrous peat. For shallow stabilization of fibrous peat, strength evaluation tests were unconfined compressive strength (UCS), and California bearing ratios (CBR), and for deep stabilizations, consolidation undrained triaxial (CU), and Rowe cell consolidation tests. Other tests started with field identification, and field vane shear, and continued in the laboratory with: sieve analysis, consistency limits, linear shrinkage, pH, compaction, hydraulic conductivity, scanning electron microscopy, energy dispersive x-ray analysis. Disturbed and undisturbed samples were used for various types of test.
For shallow stabilization, three types of curing technique have been studied for their effectiveness as well as their ease of applicability in the field. Curing techniques were: moist curing, moist curing with surcharge load and air curing. Curing periods used were 0 (immediately after mixing), 7, 28, 90, and 180 days. Based on the results obtained from three types of curing technique, air curing was chosen to be used for the entire shallow stabilization research investigation. Optimum dosage rates for
polypropylene fibres, silica fume, blast furnace slag, and fly ash used as additives for shallow or deep stabilization were determined through trial and error on UCS samples.
Strength evaluation tests were conducted on air cured samples under un-soaked and soaked conditions. Soaking to complete saturation was conducted manually and used for soaked strength evaluations of stabilized samples. In order to examine the applicability of the stabilization method used in the research in the field, fibrous peat at field moisture content was used for stabilized samples.
Also, in order for the shallow stabilization process to be more effective, stabilized samples were tested for their strength at their optimum moisture content (OMC) found from compaction curves. For deep stabilization of fibrous peat deposits, precast stabilized columns were developed and tested for their effect on improving shear strength parameters, as well as on reducing the compressibility of fibrous peat.
The process of making precast stabilized peat columns included mixing fibrous peat with a specified amount of OPC (with or without additives) at their optimum moisture content (found from compaction curves). Each type of mixture was then compacted into moulds and left to dry. As the stabilized columns dried out, due to chemical reactions and dehydration they gained strength. When drying was complete, they were taken out of their moulds and inserted into pre-drilled holes within the undisturbed fibrous peat, and tested for their strength as well as their deformation through CU triaxial and Rowe cell consolidation tests, respectively.
Precast stabilized peat columns made from hemic and sapric peats were also evaluated for strength and deformation using CU triaxial and Rowe cell consolidation tests, as well. Also, Precast stabilized fibrous peat columns were tested for load bearing capacity in larger scale (820 mm dia. and 1000 mm
198
length) in a designed and fabricated steel test tank. Untreated fibrous peat as well as six different types of precast stabilized fibrous peat columns were tested in the test tank.
Precast stabilized peat column production can be compared with precast concrete structural components prepared outside the construction site and, upon completion, they were delivered and used in site as structural members. Their productions require relatively small amounts of OPC and the usual additive (if used), compared with columns cast in-situ, but provide higher strength values and therefore more load-bearing capacity. Since the production process does not waste much of the material involved and does not use any infill materials, the columns can also be considered environmentally friendly.
All types of test results used during the course of this study indicate that stabilization procedures used in either shallow (mass) or deep stabilization improve the load bearing capacities of untreated fibrous peat, hence upgrading its engineering properties from very soft and problematic to less problematic. Use of polypropylene fibres, the combined use of polypropylene and steel fibres and silica fume helped the stabilized fibrous peat to gain strength further. Use of blast furnace slag and fly ash as additives to various types of OPC treated fibrous peat samples while being effective enough to increase strengths and decrease deformations of untreated fibrous peat, they were not as effective in providing extra strength or less compressibility to fibrous peat as the three other types of additives.
Specific finding that are presented in the following sections are listed according to the list of objectives, as well as the results stated and shown in chapter one and four respectively. Also, each main section is followed by its concluding subsections remarks investigated from the study.
199
1- Engineering properties of untreated fibrous peat
a) The shapes of particle size distribution curves for different peat may be very similar to sandy soils b) Peat may also be described as having an unusually high liquid limit (over 160%) while still being non-plastic (N.P) 2- Air cured OPC treated fibrous peat strength gain versus conventional curing techniques during 180 days
a) The most effective method to improve UCS of OPC treated fibrous peat up 30% cement is air curing technique compared with conventional techniques (moist curing, and moist curing with surcharge load of 10 kPa) b) The most effective curing method to improve UCS of OPC treated fibrous peat with 50% cement is moist curing with surcharge load of 10 kPa compared with air curing, and moist curing techniques c) The least effective method to improve UCS of OPC treated fibrous peat is moist curing technique compared with other two methods d) As the air curing period is continued through 180 days more UCS are gained 3- Strength gain of OPC treated fibrous peat when used with the following additives: i) Polypropylene fibres a) Presence of polypropylene fibres in OPC treated fibrous peat makes them to be more uniform and intact, compared with their counterparts without fibres
200
b) The most effective dosage rate among 0.1, 0.15, 0.2, and 0.5% polypropylene fibres to increase the strength of stabilized fibrous peat is 0.15% c) The shortest soaking time period for complete saturation with up to 50% OPC and 0.15% polypropylene fibres treated stabilized fibrous peat is 7 days d) Addition of polypropylene fibres as a none chemically active additive to air cured, OPC treated fibrous peat increases the UCS, and CBR values further by providing additional inner coherence to the particles bonds compared when only OPC is used to treat fibrous peat e) Lowering the natural moisture contents of fibrous peat close to optimum moisture content (OMC), and compacting the OPC treated fibrous peat with or without polypropylene fibres to their maximum dried densities (MDD) will increase UCS and CBR values significantly through air curing technique f) Immediate (after mixing) liquid limits in stabilized fibrous peat continue to reduce when the amount of OPC is increased in the mixture. The inclusion of additives polypropylene fibres reduces the LL values further g) Stabilized fibrous peat in their immediate (after mixing) condition with up to 50% OPC with or without polypropylene fibres show no sign of plastic limit and are classified non-plastic (N.P) ii) Silica fume a) Presence of silica fume in OPC treated fibrous peat makes them to be more brittle, compared with their counterparts without silica fume when subjected to imposed loads
201
b) The most effective dosage rate between 5 and 10% silica fume as an additive in OPC treated fibrous peat is 10% when less than 25% OPC is used, and 5% when 25% and above OPC is used. c) Immediate (after mixing) liquid limits in stabilized fibrous peat continue to reduce when the amount of OPC is increased in the mixture. The inclusion micro silica reduces the LL values further d) Stabilized fibrous peat in their immediate (after mixing) condition with up to 50% OPC with or without silica fume show no sign of plastic limit and are nonplastic (N.P) e) The inclusion of silica fume in 90 days air cured, OPC treated fibrous peat increases the UCS, and CBR values of air cured fibrous peat further iii)Steel fibres a) Inclusion of 2 or 4% steel fibres as none chemically active additive in air cured OPC treated fibrous peat increases the UCS, and CBR values of treated peat b) Steel fibres when used in combination with polypropylene fibres add extra strength to air cured OPC treated fibrous peat iv) Blast furnace slag
a) Blast furnace slag may be partially replaced cement amount to stabilize fibrous peat b) General trend of air cured UCS and CBR values of only OPC treated fibrous peat are higher than those with the inclusion of blast furnace slag
202
v) Fly ash a) Fly ash may be partially replaced cement amount to stabilize fibrous peat b) General trend of air cured UCS and CBR values of only OPC treated fibrous peat are higher than those with the inclusion of fly ash
4- Precast stabilized peat columns i) Reinforcing fibrous peat with precast stabilized peat columns will have the following impacts on the untreated fibrous peat; a) Increases the strength, and decrease its deformation b) Addition of polypropylene fibres or silica fume adds to strengths, and reduces deformations further c) Addition of blast furnace slag or fly ash to OPC treated peat columns increase the stability of untreated fibrous peat, but not as much as when OPC alone is used to make the columns d) OPC treated columns made of fibric, or hemic peats are as effective as columns made of fibric peat to increase stabilities of untreated fibrous peat ii) Load bearing capacity of precast stabilized peat columns increases if any of the following measures are taken; a) OPC amounts increases b) Polypropylene used as an additive c) Silica fume used as an additive d) Jointly use of polypropylene, and steel fibres as additives e) The diameter of column is increased
203
Also, some of the concluding remarks that are more general and are applicable to the stabilization of fibrous peat include the followings: a) UCS, and CBR values of unsoaked (temporary stabilized) air cured treated fibrous peat increase as the amounts of OPC in the mixture increase. This increasing trend may not apply to when 5% OPC or less is used for treatment b) UCS, and CBR values of soaked air cured treated fibrous peat increase as the amount of OPC increases in the mixture c) Use of air curing technique or precast columns to stabilize fibrous peat involves volume changes which its size depends on the amounts of OPC, or the type of additives used for stabilization. This change in volume can be evaluated by “linear volume shrinkage” or LVSI
5.2
Recommendations for future researches
Air curing as a technique to stabilize shallow depth of peat deposits (top 20 to 30 cm.) and also precast stabilized peat columns as another method for deeper stabilization to improve load bearing capacity of weak grounds such as fibrous peat can be studied further. Each study may be concentrated on durability, and applicability in the field of each particular method. Some of the specific studies that can be conducted in this regards may include; a) Use of air curing with a surcharge load to stabilize peat (fibric, hemic or sapric) with ordinary Portland cement and with or without various additives. b) Reducing the natural moisture content of peat through any practical method such as microwave heating prior to stabilization, which provides good ground for mass stabilization with the least amount of binding agent such as OPC. c) Use of various types of polypropylene fibre (e.g. longer size than used in this research) to reinforce air cured stabilized peat. 204
d) Combination of additives to stabilize peat (e.g. silica fume and polypropylene fibres). e) Finding a relationship between air curing period and strength gain for various types of stabilized peat treated with OPC. f) Use of the mass stabilization technique used in this study in conjunction with precast columns to strengthens peat deposits. g) Effect of curing time on air cured, peat treated with OPC, blast furnace slag and fly ash, considering these two additives to make the OPC treated peat to be late setting. h) More durability types of tests on various types of air cured stabilized peat, as well as precast stabilized peat columns. i) Use of sand fillers and air curing in conjunction with OPC to stabilize peat . j) Evaluations of compressibility behaviours of precast stabilized peat columns reinforcing fibrous peat using compressibility parameters such as secondary compression index, law of compressibility, or coefficient of volume compressibility values.
205
206
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216
APPENDIX A
217
Figure A1: Various types of additives used in the research
218
SEM, EDX TEST RESULTS FOR RAW MATERIALS SEM and EDX test results for various types of raw materials used in this research are shown in Figures A2 through A5. Each obtained result is followed by the tabulated chemical and physical properties of each material (Tables A1 to A4) provided by the manufactures.
Figure A2: SEM and EDX of ordinary Portland cement
Table A1: Chemical and physical properties of ordinary Portland cement ( SCANCEMENT MATERIALS 2007)
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Figure A3: SEM and EDX of silica fume Table A2: Chemical and physical properties of silica fume (SCANCEMENT MATERIALS 2007)
Figure A4: SEM, EDX of ground granulated blast furnace slag
220
Table A3: Chemical and physical properties of ground granulated blast furnace slag ( SLAG CEMENT 2008)
Figure A5: SEM, EDX of pulverised – fuel ash (fly ash) Table A4: Chemical and physical properties of pulverised – fuel ash (fly ash) (SLAG CEMENT 2008)
221
Samples with polypropylene fibres
Figure A6: UCS samples with and without polypropylene fibres
Figure A7: Failure shapes on two types of columns after load bearing tests
222
Figure A8: Simultaneous triaxial and, Rowe cell tests with a single computer in progress
Figure A9: General view of the sampling site
223
Figure A10: Various sizes of thin walled cutters prepared to make holes in the undisturbed peat to install columns (L), and in-place OPC treated columns while being moist cured for Rowe cell tests (R)
224
APPENDIX B
225
(Sample calculations)
Table B1: Consolidated undrained triaxial test
226
Table B2: Consolidated undrained triaxial test
Figure B1: p versus q values for undisturbed fibrous peat
sin α = tan φ c = α / cos φ
227
Table B3: Rowe cell consolidation test
Log time (seconds) 100
1000
10000
Deformation (mm)
100000 90 80 70 60 50 40 30 20 10 0
17 17.5 18 18.5 19 19.5 20 Deformation
Pore pressure (kPa)
10 16.5
Pore pressure
Figure B2: Log time (seconds) versus deformation (mm) and pore pressure values for undisturbed fibrous peat 228
Table B4: Rowe cell consolidation test
12 11.5
Void ratio (e)
11 10.5 10 9.5 9 8.5 8 7.5 7 10
100 Log pressure (kPa)
1000
Figure B3: Log pressure (kPa) versus void ratio values for undisturbed fibrous peat
229
Table B5: Rowe cell consolidation test
4.4 Void ratio (e)
4.2 4 3.8 3.6 3.4 3.2 3 10
100
1000
Log pressure (kPa)
Figure B4: Log. pressure (kPa) versus void ratio values for undisturbed fibrous peat reinforced with 15% OPC treated precast sapric column
230
Table B6: Unconfined compressive strength (UCS)
Figure B5: Stress – strain curves for two identical UCS stabilized fibrous peat samples treated with 15% OPC and cured for 300 days qu(1) = 446 kPa, qu(2) = 412 kPa (qu(av) = 429 kPa 231
Table B7: California bearing ratio (CBR)
Penetration (mm) 2.5 5 7.5 10
Standard load (MPa) 6.9 10.3 13 16
Figure B6: Load (kN) versus penetration (mm) to evaluate unsoaked CBR value for stabilized fibrous peat with 5% OPC and 10% silica fume, and air cure for 90 days CBR2.5 = 71%, CBR5 = 76%, CBR7.5 = 65%
232
APPENDIX C
233
Figure C1: FEM analysis for untreated peat 234
Figure C2: FEM analyses for reinforced peat with 200 mm precast stabilized peat column
235
Figure C3: FEM analyses for reinforced peat with 300 mm precast stabilized peat column
236
APPENDIX D
237
Table D1: Degree of Humification of Peat (von Post and Granlund 1926) --------------------------------------------------------------------------------------------------------------------------------von Post Scale H1 H2 H3 H4 H5 H6 H7
H8
H9 H10
Description
Completely un-decomposed peat which, when squeezed, releases almost clear water. Plant remains easily identifiable. No amorphous material present. Almost entirely un-decomposed peat which, when squeezed, releases clear or yellowish water. Plant remains still easily identifiable. No amorphous material present. Very slightly decomposed peat which, when squeezed, releases very muddy brown water, but from which no peat passes between the finger. Plant remains still identifiable and no amorphous material present. Slightly decomposed peat which, when squeezed, releases very muddy dark water. No peat is passed between the fingers but the plant remains are slightly pasty and have lost some of their identifiable features. Slightly decomposed peat which, when squeezed, releases very muddy dark water. No peat is passed between the fingers but the plant remains are slightly pasty and have lost some of their identifiable features. Moderately decomposed peat which a very indistinct plant structure. When squeezed, about one-third of the peat escapes between the fingers. The structure more distinctly than before squeezing. Highly decomposed peat. Contains a lot of amorphous material with very faintly recognizable plant structure. When squeezed, about one - half of the peat escapes between the fingers. The water, if any is released, is very dark and almost pasty. Very highly decomposed peat with large quantity of amorphous material with very indistinct plant structure. When squeezed, about two thirds of the peat escapes between the fingers. A small quantity of pasty water may be released. The plant material remaining in the hand consists of residues such as roots and fibres that resist decomposition. Practically fully decomposed peat in which there is hardly any recognizable plant structure. When squeezed it is fairly uniform paste. Completely decomposed peat with no discernible plant structure. When squeezed, all the wet peat escapes between the fingers.
238
Table D2 (a): Symbols, and descriptions of tested samples
Table D2 (b): Symbols, and descriptions of tested samples
239
Table D2 (c): Symbols, and descriptions of tested samples
Table D2 (d): Symbols, and descriptions of tested samples
240
Table D3: Field tests conducted at the field
Table D3 (a): Physical property tests programmes of untreated (plain) peat
Table D3 (b): Physical, and chemical property tests programmes of various materials
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Table D4 (a): Physical property tests programmes of treated peats
Table D4 (b): Physical property tests programmes of treated peat
Table D4 (c): Physical property tests programmes of treated peat
242
Table D4 (d): Physical, and chemical tests programmes of treated peat samples
Table D5: Mechanical property tests programmes of untreated (plain) fibrous peat
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Table D6 (a): Test programs for various types of OPC, PP-fibres, and silica fume treated peat at peat’s natural moisture contents
Table D6 (b): Test programs for various types of OPC, blast furnace slag, and fly ash treated peat at peat’s natural moisture contents (cured for 90 days)
*And means a second and a separate test with the specified amount of BFslag (B)
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Table D7 (a): Test programs for various types of OPC, PP-fibres, silica fume and blast furnace slag treated peat at mixtures optimum moisture contents
Table D7 (b): Test programs for various types of OPC, PP-fibres, steel fibres and joint use of PP, and steel fibres treated peat at mixtures optimum moisture contents
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Table D8 (a): UCS test programmes for air cured, OPC treated peat at peat’s natural moisture contents
Table D8 (b): UCS test programmes for moist cured, OPC treated peat at peat’s natural moisture contents
Table D8 (c): UCS test programmes for moist cured, OPC treated peat at peat’s natural moisture contents
246
Table D9: CU triaxial and Rowe cell consolidation tests programmes of various types of samples (undisturbed fibrous peat, and undisturbed fibrous peat containing different types of columns)
Table D10: Load bearing capacity tests programmes for various types of precast stabilized peat columns
247
Table D11: Results for obtained coefficient of compression and recompression indices for various types of precast columns reinforcing fibrous peat Types of column reinforcement
undisturbed fibrous peat Fpeat+5%OPC Fpeat+15%OPC Fpeat+30%OPC Fpeat+50%OPC Fpeat+5%OPC+0.15% PPF Fpeat+15%OPC+0.15% PPF Fpeat+30%OPC+0.15%PPF Fpeat+5%OPC+10%SFU Fpeat+15%OPC+10%SFU Fpeat+30%OPC+5%SFU Fpeat+7.5%OPC+7.5%FA Fpeat+11.25%OPC+3.75%BFSlag Sapeat+15%OPC Sapeat+15%OPC+0.15%PPF Sapeat+15%OPC+10%SFU Hpeat+15%OPC+0.15%PPF Hpeat+15%OPC+10%SFU
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Settlement Indices Cc Cr
3.64 2.3 1.63 1.5 1.44 1.893 1.56 1.413 2.1 1.58 1.42 2.08 2.63 1.677 1.26 1.36 1.441 1.467
0.49 0.218 0.166 0.11 0.105 0.24 0.167 0.122 0.268 0.167 0.117 0.167 0.257 0.2514 0.123 0.144 0.121 0.166
Table D12: Results for obtained unconfined compressive strengths values for various types of stabilized fibrous peat samples containing different moisture contents Samples types
UCS (kPa)
Plain fibrous peat Fib. Pt + 5% OPC Fib. Pt + 15% OPC Fib. Pt + 30% OPC Fib. Pt + 50% OPC Plain fibrous peat + 0.15% pp fibres Fib. Pt + 5% OPC + 0.15% pp fibres Fib. Pt + 15% OPC + 0.15% pp fibres Fib. Pt + 30% OPC + 0.15% pp fibres Fib. Pt + 50% OPC + 0.15% pp fibres Fib. Pt + 5% OPC + 10% silica fume Fib. Pt + 15% OPC + 10% silica fume Fib. Pt + 25% OPC + 10% silica fume Fib. Pt + 5% OPC + 2% steel fibres Fib. Pt + 5% OPC + 2% steel fibres + 0.15% pp fibres Fib. Pt + 15% OPC + 2% steel fibres Fib. Pt + 15% OPC + 2% steel fibres + 0.15% pp fibres Fib. Pt + 5% OPC Fib. Pt + 15% OPC Fib. Pt + 30 OPC Fib. Pt + 2.5% OPC + 2.5% Blast furnace slag Fib. Pt + 3.75% OPC + 1.25% Blast furnace slag Fib. Pt + 3.75% BFS + 1.25% OPC Fib. Pt + 7.5% OPC + 7.5% BFS Fib. Pt + 11.25% OPC + 3.75 % Blast furnace slag Feb. Pt + 11.25% BFS + 3.75% OPC Fib. Pt + 15% OPC + 15% BFS Fib. Pt + 22.5% OPC + 7.5% Blast furnace slag Fib. Pt + 22.5% BFS + 7.5% OPC Fib. Pt + 2.5% OPC + 2.5% Flay ash Fib. Pt + 3.75% OPC + 1.25% Fly ash Fib. Pt + 3.75% Fly ash + 1.25% OPC Fib. Pt + 11.25% OPC + 3.75% Fly ash Fib. Pt + 11.25% Fly ash + 3.75% OPC Fib. Pt + 22.5% OPC + 7.5% Fly ash Fib. Pt + 22.5% Fly ash + 7.5% OPC Fib. Pt + 7.5% OPC + 7.5% Fly ash Fib. Pt + 15% OPC + 15% Fly ash
Unsoaked 170*, 210*** 310*, 287** 316*** 190*,300**, 283*** 320* 560* 240* 400*, 367*** 270*, 386*** 420* 561* 320** 330** 332** 332*** 772.5*** 523*** 746*** 242* 162* 240* 186* 240* 230* 138* 174* 121* 224* 245* 214* 210* 210* 190* 110* 126* 198* 158* 140* 203*
Soaked 0*, 42*** 79*, 80** 104*** 75*, 96**, 173*** 250* 315* 39* 90*, 204*** 110*, 289*** 290* 358* 130** 165** 268.5** 116.8*** 256.8*** 210*** 354.8***
* Samples with 190 to 200% moisture content (natural moisture content of the top layer of soil) ** Samples with 187 to 192 % moisture contents (natural moisture content of the top layer of soil) *** Samples with optimum moisture contents values (found from compaction curves)
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