GEOSINTETIK INDONESIA 2016, Geosynthetics Conference Jakarta ...

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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





















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

√ √ √



Geosynthetic reinforcement Degradation and methods of assessment



√ √

Design parameter







RFID RFCH & RFW



 US Practice: AASHTO R69-2015

√ √ √ √



“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

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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

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Control

Control

10 years exposure

10 year exposure

0

0 0

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4

8 12 Strain (%)

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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

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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

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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

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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 (