direct evaluation of effectiveness of prefabricated vertical drains in liquefiable sand wen-jong...

Direct Evaluation of Effectiveness Direct Evaluation of Effectiveness of Prefabricated Vertical Drains in of Prefabricated Vertical Drains in

Liquefiable SandLiquefiable Sand

Wen-Jong Chang, National Chi Nan UniversityWen-Jong Chang, National Chi Nan UniversityEllen M. Rathje, University of Texas at AustinEllen M. Rathje, University of Texas at Austin

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

Brady R. Cox, University of Texas at AustinBrady R. Cox, University of Texas at Austin

U.S.-Taiwan Workshop on Soil Liquefaction

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

OutlineOutline

IntroductionIntroduction Drainage TechniquesDrainage Techniques Experiment MethodologyExperiment Methodology Test ResultsTest Results ConclusionConclusion

IntroductionIntroduction

Liquefaction-induced damages:Liquefaction-induced damages:

Key role: pore pressure generationKey role: pore pressure generation

Mitigation MethodsMitigation Methods

1.1. Reducing the excess pore pressure Reducing the excess pore pressure generationgeneration

Densification: dynamic compaction etc. Densification: dynamic compaction etc. Reinforcement: compaction grouting etc.Reinforcement: compaction grouting etc.

2.2. Quickly remove the accumulated pore Quickly remove the accumulated pore water pressure water pressure

Drainage: gravel drains, stone columns, Drainage: gravel drains, stone columns, prefabricated vertical drains prefabricated vertical drains

Combination of both effects

Research SignificancesResearch Significances

Problems of conventional gravel drainsProblems of conventional gravel drains mixing, clogging, installation disturbance mixing, clogging, installation disturbance

Advantages of prefabricated drainsAdvantages of prefabricated drains minimum mixing, better discharge and minimum mixing, better discharge and

storage capacity, developed sites storage capacity, developed sites applicable applicable

Goals: Goals: Quantitatively Quantitatively evaluate the evaluate the effectiveness of drainage effectiveness of drainage alonealone

Drainage Techniques : Drainage Techniques : Analytical BackgroundAnalytical Background

Seed and Booker: develop chart-based Seed and Booker: develop chart-based approachapproach

Onoue et al. : consider drain resistance,Onoue et al. : consider drain resistance, chart-based approach chart-based approach

Pestana et al. : includes drain resistancPestana et al. : includes drain resistance and reservoir capacity, FEM code (Fe and reservoir capacity, FEM code (FEQDrain)EQDrain)

Drainage Techniques : Drainage Techniques : Experimental WorksExperimental Works

Onoue et al. : large-scale in situOnoue et al. : large-scale in situ

experimentsexperiments Iai et al. : shaking table testIai et al. : shaking table test Yang and Ko : centrifuge test on aYang and Ko : centrifuge test on a

trench shape drain trench shape drain Brennan and Madabhushi : centrifuge Brennan and Madabhushi : centrifuge

test on a “cell”test on a “cell”

Field Performance of Gravel Field Performance of Gravel Drains Drains

Japan’s experiences: sand drains performeJapan’s experiences: sand drains performed well in 1993 Kushiro-Oki and 1995 Hyogod well in 1993 Kushiro-Oki and 1995 Hyogoken-Nambu EQ.ken-Nambu EQ.

Sand drains reduced ground settlements mSand drains reduced ground settlements more than 50% ore than 50%

Performance cannot be solely attributed to Performance cannot be solely attributed to drainage drainage

Prefabricated Drains Prefabricated Drains

Components:Components:

Features: Features: better discharge capacity & storage better discharge capacity & storage

capacities capacities

Installation: Installation: statically/dynamicallystatically/dynamically Rollins et al. blasting test: Rollins et al. blasting test:

reducing reducing 40~80%40~80% settlements settlements

11.8 cm O.D.

0.64 cm

1.1 cm

10.5 cm

Slots at Quarter Points of DrainSlots Measure .0.13 cm x 2.16 cm

Open slot

Filter fabric

Plastic pipe

Experiment Methodology Experiment Methodology

Two full-scale reconstituted Two full-scale reconstituted specimens specimens

In situ dynamic liquefaction testIn situ dynamic liquefaction test Data reductionData reduction Test setupTest setup

In Situ Dynamic Liquefaction In Situ Dynamic Liquefaction Test Test

Components: Components: Dynamic source : Vibroseis truckDynamic source : Vibroseis truck Embedded instrumentation: LiquefactioEmbedded instrumentation: Liquefactio

n test sensor & DAQ n test sensor & DAQ Test layoutTest layout

Hydraulic Ram

Vibroseis Truck

Horizontal Geophone

Pore Pressure Transducer

Filter

Cable

Shoe

Vertical

Geo

ph

on

e

8.9 cm

2.5 cm

3.8 cm

Liquefaction Test Sensor

Backfill soil

3.3 m

Footing

Vibroseis truck

Waterproof liner

1 2

3 4

1.2 m

1.2 m0.3 m

0.3 m

0.3 m 0.3 m

5Liquefaction sensor

Accelerometer

Settlement platform

PVC pipe

Test Layout

Data AnalysisData Analysis

Pore pressure data: separate Pore pressure data: separate staticstatic, , hydrodynamichydrodynamic, , and and residual excess poreresidual excess pore pressure via digital filter pressure via digital filter

Shear strain calculation:Shear strain calculation: Displacement-Based (DB) method Displacement-Based (DB) method

Apparent Wave (AW) methodApparent Wave (AW) method

Pore pressure generation curve & time historiesPore pressure generation curve & time histories

B u

vxz

ah

PV

V

Test SetupTest Setup

1.17 m

1.2 m

3.3 m

Foundation

Vibroseis truck

0.3 m

Waterproof liner

1 2

4

5

3

0.3 m

0.29 m

0.3 m

0.31 m

0.27 m

0.9 m

Backfill sand

Legend

Liquefaction Test Sensor

Settlement Plate

Legend

Liquefaction Test Sensor

Settlement Plate

1.15 m

1.2 m

3.3 m

Foundation

Vibroseis truck

0.23 m

Waterproof liner

2 4 5 3

0.3 m 0.46 m

0.7 m

Backfill sand

0.69 m

1

0.15 m

Drain Pipe

No Drain Test Drain Test

Drain pipe

Specimen PreparationSpecimen Preparation

Both specimens using water pluviation to Both specimens using water pluviation to construct loose, saturated specimensconstruct loose, saturated specimens

Prefabricated drain were installed prior wPrefabricated drain were installed prior water pluviation ater pluviation no densificationno densification

Sensors were installed during water pluviSensors were installed during water pluviation processation process

Testing ProcedureTesting Procedure

Loading frequency=20 Hz for 3 secondsLoading frequency=20 Hz for 3 seconds Interactive stage loading:Interactive stage loading:

From small loading to largest loading levelFrom small loading to largest loading level Fully dissipation of excess pore pressure Fully dissipation of excess pore pressure

between loadingbetween loading Determine threshold shear strainDetermine threshold shear strain Generate pore pressure generation curveGenerate pore pressure generation curve

Test Results:Test Results:Pore Pressure Generation CurvePore Pressure Generation Curve

100

80

60

40

20

0

Exc

ess p

ore

pres

sure

ratio

, Ru

(%)

0.0001 0.001 0.01 0.1

Mean shear strain amplitude (%)

No Drain Test Drain Test

Dr = 36%

n = 60 cycles

Threshold shear strain

Time HistoriesTime Histories

-20

-10

0

10

20

She

ar S

trai

n (x

10-3

%)

43210Tim e (s ec)

No Drain Tes tSens or 5Depth=0.56 m

-20

-10

0

10

20

Shea

r St

rain

(x1

0-3 %

)

43210Time (sec)

Drain TestSensor 4Depth=0.69 m

120

100

80

60

40

20

0

Ru (

%)

43210Time (sec)

No Drain TestSensor 5Depth=0.56 m

100

80

60

40

20

0

-20

Ru (

%)

43210Time (sec)

Drain TestSensor 4Depth=0.69 m

No Drain Test Drain Test

Dissipation Behavior Dissipation Behavior 40

30

20

10

0

Ru,

(%

)

1086420Time (sec)

Within drain R=0.10 m R=0.25 m R=0.48 m R=0.78 m

Ru-time histories at different radial distances

Dissipation RateDissipation Rate

100

80

60

40

20

0

Ru,

(%

)

1086420Time (sec)

No Drain Test Drain Test

ConclusionsConclusions

Drainage Drainage alonealone can considerably can considerably reduce pore pressure generationreduce pore pressure generation minimize settlementminimize settlement accelerate after shaking dissipationaccelerate after shaking dissipation

With single prefabricated drain, max. With single prefabricated drain, max. pore pressure ratio only 35% instead of pore pressure ratio only 35% instead of 100% in No Drain Test100% in No Drain Test

Conclusions (cont.)Conclusions (cont.)

Drainage Drainage alonealone can reduce volumetric can reduce volumetric strain up to 75%strain up to 75%

Prefabricated drain can be an effective Prefabricated drain can be an effective alternative for liquefaction mitigationalternative for liquefaction mitigation

Same testing procedure can be Same testing procedure can be implemented to evaluate other implemented to evaluate other remediation techniques and current remediation techniques and current treated sitestreated sites

Thank YouThank You

Research Supported byResearch Supported by

National Science FoundationNational Science Foundation