Jakarta, Indonesia. 10th May 2016. Paper 8: Design parameters for geosynthetic reinforcement: Michael Dobie. 1. Tensar International Limited. Regional ...
GEOSINTETIK INDONESIA 2016, Geosynthetics Conference Jakarta, Indonesia
10th May 2016
Design methods
GEOSINTETIK INDONESIA 2016 Jakarta, 10th May 2016
Reinforced soil structures Three main components
Calculation procedure: Session 2 Material parameters: Fill properties in Session 2 Factors: Sessions 1
Design Parameters and Specification for Geosynthetic (Polymer) Reinforcement Mike Dobie Tensar International Limited Regional Manager Asia Pacific
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Design Parameters and Specification for Geosynthetic Reinforcement
Failures
Failures
Reason for failure? Material or design or system failure…….
Reason for failure? Material or design or system failure…….
Design Parameters and Specification for Geosynthetic Reinforcement
10th May 2016
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Design Parameters and Specification for Geosynthetic Reinforcement
Failures
Failures
Reason for failure? Material or design or system failure…….
Reinforced soil structures Which component is responsible?
10th May 2016
10th May 2016
Calculation procedure? Material parameters? Factors? This can only be identified by careful investigation But the component over which we have most control is the geosynthetic reinforcement
Made in a factory Extensively tested
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Design Parameters and Specification for Geosynthetic Reinforcement
10th May 2016
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Design Parameters and Specification for Geosynthetic Reinforcement
Paper 8: Design parameters for geosynthetic reinforcement: Michael Dobie
10th May 2016
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GEOSINTETIK INDONESIA 2016, Geosynthetics Conference Jakarta, Indonesia
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10th May 2016
Soil structures
Soil structures
Slope (1:2) All resistance from soil
Slope (1:1) Most resistance from soil, less from reinforcement
Soil strength required
Soil strength required Also design parameters for reinforcement
Design Parameters and Specification for Geosynthetic Reinforcement
10th May 2016
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Design Parameters and Specification for Geosynthetic Reinforcement
10th May 2016
Soil structures
Soil structures
Retaining wall (vertical) Most resistance from reinforcement, less from soil
Retaining wall (vertical) Contributions to resistance from reinforcement
Soil strength required Also design parameters for reinforcement and facing
Look at 2-part wedge which slides over reinforcement
Sliding interaction, fds
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Design Parameters and Specification for Geosynthetic Reinforcement
10th May 2016
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Design Parameters and Specification for Geosynthetic Reinforcement
10th May 2016
Soil structures
Properties of geosynthetic reinforcement
Retaining wall (vertical) Contributions to resistance from reinforcement
Defining allowable design strength ULS static European practice
Look at 2-part wedge which intersects the reinforcement TD(ULS) required to meet the requirements of the climate
ULS design strength of geosynthetic reinforcement:
and environment of Indonesia
Connection strength with facing Tconn
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TD(ULS) = long term design strength for ULS Tchar = characteristic tensile strength RFCR = creep reduction factor = Tchar/TCR RFID = installation damage factor RFW = factor for weathering RFCH = factor for chemical & environmental effects fs = factor for extrapolation of data fn = factor to take account of consequence of failure (BS 8006)
Pull-out interaction, fb Design strength, TD(ULS)
Design Parameters and Specification for Geosynthetic Reinforcement
10th May 2016
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Design Parameters and Specification for Geosynthetic Reinforcement
Paper 8: Design parameters for geosynthetic reinforcement: Michael Dobie
10th May 2016
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GEOSINTETIK INDONESIA 2016, Geosynthetics Conference Jakarta, Indonesia
Properties of geosynthetic reinforcement Property
Concerns? F
Identification (I) Dimensions (I) Quality control Tensile strength (I) Tensile creep strength Junction strength Installation damage (I) Durability Carbon black content Connection (I) Connection to facing Interaction with fill (I) Post-construction deformation Aesthetics
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O
Two important European codes: EN 13251 “Geotextiles and geotextile-related products – Characteristics required for use in earthworks, foundations and retaining structures” ISO/TR 20432 “Guidelines for the determination of the long-term strength of geosynthetics for soil reinforcement”
Tchar TCR, RFCR
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Geosynthetic reinforcement Degradation and methods of assessment
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Design parameter
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RFID RFCH & RFW
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US Practice: AASHTO R69-2015
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“Standard practice for determination of long-term strength of geosynthetic reinforcement”
Tconn fds & fb TCS
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Design Parameters and Specification for Geosynthetic Reinforcement
Degradation of geosynthetic reinforcement
Geosynthetic reinforcement Degradation and methods of assessment
Creep Determination of TCR, TCS and RFCR
Mode 1: immediate
Creep tests Simple test
reduction in strength after a long period, reduce service life (do not use RF)
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Details such as
Mode 3
Mode 2
temperature control and clamping vital to obtaining representative results
Mode 1
Time (years)
Design Parameters and Specification for Geosynthetic Reinforcement
10th May 2016
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Design Parameters and Specification for Geosynthetic Reinforcement
Degradation of geosynthetic reinforcement
Degradation of geosynthetic reinforcement
Creep tests which are taken down before rupture Compare tensile strength before and after test
Creep Determination of TCR, TCS and RFCR
110
100
100
80 70 60 50 10°C 20°C
30
30°C
20
40°C
10
50°C
Tests close to rupture
0
90 80 70 60 50 10°C
40
20°C
30
30°C
20
40°C
10
50°C
0 0
5 10 15 20 25 30 35 Strain reached in creep test (%)
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3 secs 120
Load (% of tensile strength)
90
Retained strain at failure (%)
110
40
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method
Residual property (%)
Mode 3: rapid
Retained tensile strength (%)
C
Properties of geosynthetic reinforcement
Properties of geosynthetic reinforcement
reduction in strength, use timeindependent RF Mode 2: gradual reduction in strength, use timedependent RF
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D
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0
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30 secs 1 minute
80 60 40 20
Creep rupture strength Long term strength for 120 year life Residual strength based on ISO 10319 Residual strength based on ISO 10319 x10 Residual strength based on ASTM D6637 20 deg C data from Figure 5
0
5 10 15 20 25 30 35 Strain reached in creep test (%)
Design Parameters and Specification for Geosynthetic Reinforcement
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0.0000001 0.000001 0.00001
0.0001
0.001
0.01
0.1
1
10
100
1000
Time (years) 18
Design Parameters and Specification for Geosynthetic Reinforcement
Paper 8: Design parameters for geosynthetic reinforcement: Michael Dobie
10th May 2016
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GEOSINTETIK INDONESIA 2016, Geosynthetics Conference Jakarta, Indonesia
10th May 2016
Degradation of geosynthetic reinforcement
Degradation of geosynthetic reinforcement
Creep Determination of TCR, TCS and RFCR
Weathering Determination of RFW
Question: if
Protection
tensile strength is available to end-of-life, why not use it for design? Creep is Mode 3 behaviour We need to limit load to ensure that rupture is reached at the design life 19
required
Coating Additives
(carbon black)
Limit duration of exposure
This would be Mode 3
UV exposure
level is high in Indonesia
Design Parameters and Specification for Geosynthetic Reinforcement
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Design Parameters and Specification for Geosynthetic Reinforcement
Degradation of geosynthetic reinforcement
Degradation of geosynthetic reinforcement
Weathering investigation using exposure trial Determination of RFW
Installation damage Determination of RFID
UV exposure trial in Australia after 10 years Protection using > 2% carbon black
Determined
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from full scale site damage trials
60 PP reinforcement with > 2% carbon
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Load (kN/m)
Load (kN/m)
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HDPE reinforcement with > 2% carbon
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40
20
Control
Control
10 years exposure
10 year exposure
0
0 0
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4
8 12 Strain (%)
16
0
4 8 Strain (%)
Design Parameters and Specification for Geosynthetic Reinforcement
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Degradation of geosynthetic reinforcement
Degradation of geosynthetic reinforcement
Installation damage Determination of RFID
Installation damage Determination of RFID
Determined
Determined
from full scale site damage trials
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Design Parameters and Specification for Geosynthetic Reinforcement
Design Parameters and Specification for Geosynthetic Reinforcement
10th May 2016
from full scale site damage trials Find RFID by comparing strength of damaged and control Mode 1 Using lab tests is not suitable to find RFID 10th May 2016
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Design Parameters and Specification for Geosynthetic Reinforcement
Paper 8: Design parameters for geosynthetic reinforcement: Michael Dobie
10th May 2016
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GEOSINTETIK INDONESIA 2016, Geosynthetics Conference Jakarta, Indonesia
10th May 2016
Degradation of geosynthetic reinforcement
Degradation of geosynthetic reinforcement
Chemical degradation – oxidation Determination of RFCH
Chemical degradation – oxidation Determination of RFCH
Oxidation is the main issue for polyolefins (HDPE & PP) Protection provided by anti-oxidant additives Investigation requires accelerated testing
Tests on HDPE reinforcement in autoclave Pure oxygen at 51 bar Residual strength (%)
120 100 80 60
50% residual strength
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Test conditions: specimens in water under 51 bar pressure from pure oxygen
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80 deg C 70 deg C 60 deg C
0 0
50
100
150
200
250
300
Time (days) 25
Design Parameters and Specification for Geosynthetic Reinforcement
10th May 2016
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Design Parameters and Specification for Geosynthetic Reinforcement
Degradation of geosynthetic reinforcement
Degradation of geosynthetic reinforcement
Chemical degradation – oxidation Determination of RFCH
Chemical degradation – hydrolysis Determination of RFCH
Mode 3 behaviour, so limit on service life Oxidation potential increases with increasing temperature
Residual strength (%)
120 100 80
10th May 2016
Hydrolysis is the main issue for polyester (PET) High molecular weight important to resist hydrolysis Carboxyl end group (CEG) content < 30 meq/g Number molecular weight (Mn) > 25,000 g/mol
Hydrolysis is a Mode 2 deterioration, so suitable for
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establishing reduction factors
50% residual strength
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Test conditions: specimens in water under 51 bar pressure from pure oxygen
20
80 deg C
Effect becomes more severe in extreme pH (especially alkaline conditions), and with increasing temperature
70 deg C 60 deg C
0 0
50
100
150
200
250
300
Time (days) 27
Design Parameters and Specification for Geosynthetic Reinforcement
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Design Parameters and Specification for Geosynthetic Reinforcement
Degradation of geosynthetic reinforcement
Design parameters for interaction
Chemical degradation – hydrolysis Determination of RFCH
Geogrid buried in compacted fill
RFCH accounting for hydrolysis of PET versus temperature
Interaction
from various sources
between geogrid and compacted fill Sliding, fds Pull-out, fb
2 Mak & Ng PET 1 Mak & Ng PET 2 BBA Cert No 09/R146 for 120 yrs ISO/TR 20432 for 25 years
1.8
RFCH
1.6
pH < 10 for Mak & Ng 4 < pH < 9 for BBA Cert 4 < pH < 9 for ISO/TR 20432
1.4
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1.2 1 10
20
30
40
Temperature (°C) 29
Design Parameters and Specification for Geosynthetic Reinforcement
10th May 2016
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Design Parameters and Specification for Geosynthetic Reinforcement
Paper 8: Design parameters for geosynthetic reinforcement: Michael Dobie
10th May 2016
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GEOSINTETIK INDONESIA 2016, Geosynthetics Conference Jakarta, Indonesia
10th May 2016
Design parameters for interaction
Design parameters for interaction
Sliding interaction Test in large shear box (300mm × 300mm)
Sliding interaction Test in large shear box (300mm × 300mm)
Shear box Adapted so that
Shear box Normal load
reinforcement may be fixed to lower half Fill placed in upper half
δv = vertical displacement
δh = horizontal displacement
Shear force Soil fill
Geogrid clamped in lower side of shearbox
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Design Parameters and Specification for Geosynthetic Reinforcement
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Design Parameters and Specification for Geosynthetic Reinforcement
Design parameters for interaction
Sliding interaction Typical result for sandy fill
Sliding interaction Important warning
Shear stress (kPa)
Design parameters for interaction
160
160
120
120
Shear force
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Reinforced soil design is carried out using drained analysis for all fill types
Therefore interaction factors should be measured using
φsoil 80
drained tests
80
φsoil/grid
σn = 150 kPa 40
Easy for sands and gravels
40
D85 = 2mm soil /grid D85 = 2mm soil
0
BUT test procedures could be of very long duration for
0 0
10
20 30 δh (mm)
40
50
0
40
80 120 160 Normal stress (kPa)
finer soils, such as tanah merah
200
Interpretation of test
results based on peak
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Design Parameters and Specification for Geosynthetic Reinforcement
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Sources of reinforcement design parameters
Sources of reinforcement design parameters
Option 1 Manufacturer’s specification sheets
Option 2 Published default values
Most manufacturers published specification sheets
AASHTO LRFD Bridge Design Specification in Table
which include some or all of the design data required May not be considered impartial so independent verification may be required
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Design Parameters and Specification for Geosynthetic Reinforcement
Design Parameters and Specification for Geosynthetic Reinforcement
10th May 2016
11.10.6.4.3b-1, recommends a lumped factor combining creep reduction, installation damage and durability of 7.0 In terms of the definitions used here, this means that RFCR × RFID × RFW × RCH × fs = 7.0 The conditions for this are: Soil is considered non-aggressive pH in the range 4.5 to 9 maximum particle size less than 20mm design temperature less than 30°C 36
Design Parameters and Specification for Geosynthetic Reinforcement
Paper 8: Design parameters for geosynthetic reinforcement: Michael Dobie
10th May 2016
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GEOSINTETIK INDONESIA 2016, Geosynthetics Conference Jakarta, Indonesia
Sources of reinforcement design parameters
Sources of reinforcement design parameters
Option 2 Published default values
Option 3 Published fitness-for-purpose certificates
The Australian code for earth-retaining structures gives
No system has been created in Indonesia Use an established system such as the British Board of
these suggestions in Appendix K:
Factor
Factor in AS 4678
RFCR
1/Φrc 1/Φue (2 log cycles time)
PET 2.0 1.3 RFID 1/Φri (1.7 to 1.1, use mean) 1.4 RFD = 1/Φrt (1.0 to 1.1, use mean) 1.05 1/Φrs (1.1 to 2.0, use mean) 1.55 RFW × RFCH 1/Φrst (for temperature, incl) 1.0 1/Φud (degradation) 1.25 Manufacturing 1/Φup (1.05 if based on Tchar) 1.05 7.8 Overall = RFCR × RFID × RFW × RCH × fs min 4.1
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HDPE 3.3 1.3 1.4
PP 5.9 1.3 1.4
1.05 1.55 1.0 1.25 1.05
1.05 1.55 1.0 1.25 1.05
Agrément
About 24 certificates (currently) cover a wide range of geosynthetic reinforcement and associated systems, for various applications: Retaining walls and load bearing bridge abutments Embankment slopes (