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U.S.-Taiwan Workshop on Soil Liquefaction. Direct Evaluation of Effectiveness of Prefabricated Vertical Drains in Liquefiable Sand. Wen-Jong Chang, National Chi Nan University Ellen M. Rathje, University of Texas at Austin Kenneth H. Stokoe, II , University of Texas at Austin

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direct evaluation of effectiveness of prefabricated vertical drains in liquefiable sand

U.S.-Taiwan Workshop on Soil Liquefaction

Direct Evaluation of Effectiveness of Prefabricated Vertical Drains in Liquefiable Sand

Wen-Jong Chang, National Chi Nan University

Ellen M. Rathje, University of Texas at Austin

Kenneth H. Stokoe, II , University of Texas at Austin

Brady R. Cox, University of Texas at Austin

11/03/2003~11/04/2003 @ NCTU

outline
Outline
  • Introduction
  • Drainage Techniques
  • Experiment Methodology
  • Test Results
  • Conclusion
introduction
Introduction
  • Liquefaction-induced damages:

Key role: pore pressure generation

mitigation methods
Mitigation Methods
  • Reducing the excess pore pressure generation
    • Densification: dynamic compaction etc.
    • Reinforcement: compaction grouting etc.
  • Quickly remove the accumulated pore water pressure
    • Drainage: gravel drains, stone columns, prefabricated vertical drains

Combination of both effects

research significances
Research Significances
  • Problems of conventional gravel drains
    • mixing, clogging, installation disturbance
  • Advantages of prefabricated drains
    • minimum mixing, better discharge and storage capacity, developed sites applicable
  • Goals: Quantitatively evaluate the effectiveness of drainage alone
drainage techniques analytical background
Drainage Techniques : Analytical Background
  • Seed and Booker: develop chart-based approach
  • Onoue et al. : consider drain resistance, chart-based approach
  • Pestana et al. : includes drain resistance and reservoir capacity, FEM code (FEQDrain)
drainage techniques experimental works
Drainage Techniques : Experimental Works
  • Onoue et al. : large-scale in situ

experiments

  • Iai et al. : shaking table test
  • Yang and Ko : centrifuge test on a

trench shape drain

  • Brennan and Madabhushi : centrifuge test on a “cell”
field performance of gravel drains
Field Performance of Gravel Drains
  • Japan’s experiences: sand drains performed well in 1993 Kushiro-Oki and 1995 Hyogoken-Nambu EQ.
  • Sand drains reduced ground settlements more than 50%
  • Performance cannot be solely attributed to drainage
prefabricated drains
Prefabricated Drains
  • Components:
  • Features:

better discharge capacity & storage capacities

  • Installation:

statically/dynamically

  • Rollins et al. blasting test: reducing 40~80% settlements

Open slot

Filter fabric

Plastic pipe

experiment methodology
Experiment Methodology
  • Two full-scale reconstituted specimens
  • In situ dynamic liquefaction test
  • Data reduction
  • Test setup
in situ dynamic liquefaction test
In Situ Dynamic Liquefaction Test
  • Components:
    • Dynamic source : Vibroseis truck
    • Embedded instrumentation: Liquefaction test sensor & DAQ
  • Test layout
slide12

Vibroseis Truck

Hydraulic Ram

slide14

Test Layout

Vibroseis truck

Waterproof liner

PVC pipe

Backfill soil

Footing

2

1

0.3 m

3.3 m

1.2 m

5

Liquefaction sensor

0.3 m

Accelerometer

4

3

Settlement platform

0.3 m

0.3 m

1.2 m

data analysis
Data Analysis
  • Pore pressure data: separate static, hydrodynamic, and residual excess pore pressure via digital filter
  • Shear strain calculation:
    • Displacement-Based (DB) method
    • Apparent Wave (AW) method
  • Pore pressure generation curve & time histories
test setup
Test Setup

Drain pipe

Drain Test

No Drain Test

specimen preparation
Specimen Preparation
  • Both specimens using water pluviation to construct loose, saturated specimens
  • Prefabricated drain were installed prior water pluviation  no densification
  • Sensors were installed during water pluviation process
testing procedure
Testing Procedure
  • Loading frequency=20 Hz for 3 seconds
  • Interactive stage loading:
    • From small loading to largest loading level
    • Fully dissipation of excess pore pressure between loading
    • Determine threshold shear strain
    • Generate pore pressure generation curve
time histories
Time Histories

No Drain Test

Drain Test

dissipation behavior
Dissipation Behavior

Ru-time histories at different radial distances

conclusions
Conclusions
  • Drainage alone can considerably
    • reduce pore pressure generation
    • minimize settlement
    • accelerate after shaking dissipation
  • With single prefabricated drain, max. pore pressure ratio only 35% instead of 100% in No Drain Test
conclusions cont
Conclusions (cont.)
  • Drainage alone can reduce volumetric strain up to 75%
  • Prefabricated drain can be an effective alternative for liquefaction mitigation
  • Same testing procedure can be implemented to evaluate other remediation techniques and current treated sites
thank you
Thank You

Research Supported by

National Science Foundation

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