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