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Exposicion Profesor Bray
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Soil Liquefaction
Jonathan D. Bray, Ph.D., P.E.
Faculty Chair in Earthquake Engineering Excellence University of California, Berkeley
Primary Sponsor: National Science Foundation
OUTLINE
Liquefaction Concepts
1999 Kocaeli, Turkey EQ
2010-2011 Canterbury, New Zealand EQs
Recommendations
SOIL LIQUEFACTION
LIQUEFACTION
1964 Niigata, Japan EQ (from H.B. Seed) 1906 San Francisco EQ (Lawson et al. 1908)
1989 Loma Prieta EQ
Lower San Fernando Dam- 1971 San Fernando EQ From H.B. Seed
Lower San Fernando Dam- 1971 San Fernando EQ From H.B. Seed
LIQUEFACTION EFFECTS
Flow Liquefaction Cyclic Mobility (strain-softening large strain) (strain-hardening limited strain)
LIQUEFACTION Factor of Safety (FS)
Youd et al. 2001 based on Seed et al. 1985
CRR
Liquefaction Effects Observed at Ground Surface No Liquefaction
Effects Observed at Ground Surface
FS = CRR / CSR CSR
FS =1.2
FS =1.2
LIQUEFACTION EFFECTS
Idriss & Boulanger 2008
Flow Liquefaction
Cyclic Mobility
Post-Liquefaction Residual Strength
Idriss & Boulanger 2008
15
Soil Layering: Human-Made and Geologic
Lower San Fernando Dam: H.B. Seed
Liquefaction-Induced Building Movements March 11, 2011 Tohoku, Japan Earthquake (Mw = 9.0)
Tokimatsu et al. & GEER ( Ashford et al.)
30 cm 70 cm = 30 cm + 40 cm
Measured Displacements in Model Tests
Structure B during Large Port Island event - Test 3-30 Dashti et al. 2010a & 2010b
Large Port Island Event
3 m liquefiable layer
21 m dense sand
2 m dense sand
Building Settlement in Thick Liquefiable Soil Deposits
- Dashti et al. 2010
Bray and Dashti 2010
Dashti et al. 20100
Building Settlement is not Proportional to Thickness of Liquefied Layer
DISPLACEMENT MECHANISMS 1. Volumetric Deformations
Partial Drainage (p-DR) Sedimentation (p-SED) Consolidation (p-CON)
2. Shear-Induced Deformations
Bearing Capacity Failure (q-BC)
SSI-Induced Ratcheting (q-SSI)
3. Ground Loss due to Ejecta
COMMON APPROACH: Estimate Liquefaction-Induced Free-Field Settlement of Level Ground
Ishihara & Yoshimine 1992
= (v)(h)
Dr = 60% FSl = 0.6
Dr = 40% FSl = 0.4
Dr = 90% FSl = 2.5
Nonliquefiable
Estimates 1D settlements due to post-liquefaction volumetric reconsolidation
No shear-induced displacements
Does not estimate building movement
1999 Kocaeli EQ (Mw = 7.5): Adapazari FIELD OBSERVATIONS OF LIQUEFACTION EFFECTS
Buildings Displace Relative to Surrounding Ground
166 CPT/SCPTu & 61 BORINGS with SPT
< http://peer.berkeley.edu/turkey/adapazari >
Fieldwork in Adapazari (Bray et al. 2004)
Accelerometers
Strain Gages
)()( tAEtF == dttAtV )()(
=
=
=ftt
t
dttVtFEFV0
)()(
6060
EFVNN =
Measured Force and Velocity
05
10
15
40 50 60 70 80
Energy Ratio (%)
Ro
d L
en
gth
(m
)
0
5
10
15
40 50 60 70 80
Energy Ratio (%)
Ro
d L
en
gth
(m
)
N-value = 4 N-value = 10
Correction factors
(Skempton, 1986)
Correction factors
(Skempton, 1986)
SPT Short-Rod Correction
Sancio & Bray 2005
Building Response in Adapazari - 1999 Kocaeli EQ
SITE C - Generalized Subsurface Profile D
epth
(m)
Ground Failure No Ground Failure
Photos by Idriss
20
30
40
50
60
70
0 10 20 30 40 50 60 70Percent weight corresponding to 5m
Liqu
id L
imit
SusceptibleModerate SusceptibilityNot Susceptible
Susceptible if wc > 0.9LL
Not Susceptible
Liquefaction Susceptibility of Fine-Grained Soils
Chinese Criteria (Seed & Idriss 1982; Youd et al. 2001):
Liquefaction can only occur if:
1) LL < 35 , 2) wc > 0.9 LL, & 3) Material Finer than 5 m < 15%
CTX Testing by Bray & Sancio 2006
Liquefaction Susceptibility of Fine-Grained Soils
Bray & Sanco (2006)
PI 12 & wc / LL 0.85
Ishihara (1996)
PI 10 - CRRs are similar
0
10
20
30
40
50
0.4 0.6 0.8 1.0 1.2 1.4wc/LL
Pla
stic
ity In
dex
Susceptible to LiquefactionModerate SusceptibilityNot Susceptible
Idriss & Boulanger (2008)
PI < 7
Liquefaction of Fine-Grained Soils
Bray & Sanco (2006)
cyclic response of low plasticity fine-grained soils that are similar to that of sands are also called liquefaction
Idriss & Boulanger (2008)
the term liquefaction should be used only for soils that are evaluated through penetration tests
Bray & Sancio (2008) & Boulanger & Idriss (2008) Perform cyclic tests on slightly plastic soils as undisturbed samples can be retrieved
Test because empirical field methods have limited data
Thin- Walled Piston Sampler
Undisturbed Soil Sampling & Testing
Careful Handling
Cut Extrude Test
-40-30-20-10
010203040
-5 -4 -3 -2 -1 0 1 2 3 4 5Axial Strain, a (%)
Dev
iato
r Stre
ss, q
(kP
a) J5-P3A LL = 27 PI = 7
e = 0.75
cycle 1
cycle 13
-40-30-20-10
010203040
-5 -4 -3 -2 -1 0 1 2 3 4 5Axial Strain, a (%)
Dev
iato
r Stre
ss, q
(kP
a) D5-P2A LL = 25 PI = 0
e = 0.83
cycle 1
cycle 11
-40-30-20-10
010203040
-5 -4 -3 -2 -1 0 1 2 3 4 5Axial Strain, a (%)
Dev
iato
r Stre
ss, q
(kP
a) A6-P10A LL = 44 PI = 18 e = 1.09
cycle 139
cycle 1
-40-30-20-10
010203040
-5 -4 -3 -2 -1 0 1 2 3 4 5Axial Strain, a (%)
Dev
iato
r Stre
ss, q
(kP
a) A6-P6A LL = 38 PI = 11 e = 0.94
cycle 15
cycle 1
Bray & Sancio 2006
Reconstituted
Soil Specimens
CSS Testing:
Soil G has PI = 10
PI = 2 PI = 5
PI = 11
PI = 14 PI = 7
Donahue et al. 2007
Cyclic Resistances of PI = 2 & PI = 10 Soils
Slurry Deposition CSS Testing v 137 kPa Donahue et al. 2007
Evaluation of Ic > 2.6 Criterion
A liquefaction site in Adapazari (Bray & Sancio 2009)
2.6 12 0.85
Canterbury EQs: Widespread Liquefaction
Cubrinovski et al. 2011
Liquefaction Effects in Christchurch
From M. Cubrinovski
4 Sept 2010
(Mark Quigley: Avonside; R. Green)
22 Feb 2011
16 April 2011 13 June 2011: Part
1
13 June 2011: Part 2
Repeated Liquefaction Events
CTUC Building Liquefaction-Induced Differential Settlement Induces Distress
GEER: Bray, Cubrinovski et al.
Building Settlement (cm) Maximum Angular Distortion 1 / 50
490
7 8 11 20 6
31
Ejecta
0
CTUC Building: Christchurch EQ
2011 Christchurch EQ: Robertson & Wride (1998)
N
CTUC Building Settlement
~40 cm ~15 cm
Actual Settlement
~15 cm ~10 cm ~5 cm
Robertson & Wride (1998) & Zhang, Robertson et al. (2002)
SA Building Liquefaction-Induced Differential Settlement Induces Distress
GEER: Bray, Cubrinovski et al.
2011 Christchurch EQ: Robertson & Wride (1998)
SA Building: Christchurch EQ
0 0.5 1 1.5 2
0
1
2
3
4
5
6
7
FS
Dep
th (m
)
0 5 10 15 20
0
1
2
3
4
5
6
7
Settlement (cm)
4 SEP 1026 DEC 1022 FEB 1113 JUN 11
SA Building: Sensitivity of Results
Robertson & Wride (1998) & Zhang, Robertson et al. (2002)
CPT Z8-7
Observed Settlement 10 cm - 25 cm
FSBC 1
PWC Building Liquefaction-Induced Differential Settlement and Tilt
GEER: Bray, Cubrinovski et l
21 stories on basement mat
PWC Building
2011 Christchurch EQ: Robertson & Wride (1998)
Nonlinear Effective Stress Analyses based on Testing
FLAC Analyses with UBC-Sand: Model A in Test T3-50 large P.I. event
0 1 2 3 4 5 6 7 8 9 10-30
-20
-10
0
10
20
30
Time (sec)
She
ar S
train
(%)
Arulmoli CSS TestUBCSAND1 Calibration
She
ar S
trai
n (%
)
Time (sec)
Nevada Sand CSS tests Arulmoli et al. 1992 Dr = 63%, CSR = 0.3, K = 0
Cal
cula
ted
Sett
lem
ent (
mm
)
Maximum Shear Strain
CONCLUSIONS Liquefaction can severely damaged earth structures
and buildings & utilities
Shallow liquefiable soils can lead to much building damage, especially when ejecta occurs
Cyclic mobility occurs for PI 12 & wc/LL 0.85 soil
Building settlement is not proportional to the thickness of the liquefiable layer
Shear-induced deformation is critical mechanism
Simplified procedures do not capture the observed performance of heavy structures with shallow foundations
RECOMMENDATIONS
Perform cyclic testing on fine-grained soils that can be sampled effectively to assess their seismic response characteristics.
0
10
20
30
40
50
0.4 0.6 0.8 1.0 1.2 1.4wc/LL
Pla
stic
ity In
dex
Susceptible to LiquefactionModerate SusceptibilityNot Susceptible
Liquefaction triggering procedures, which have been developed for sands and nonplastic silty sands, should be applied with judgment.
Bray & Sancio 2006
RECOMMENDATIONS For level ground conditions with no free-face:
Pile foundation with its neutral plane in firm ground below the liquefiable layer will not settle significantly
Shallow foundation with deep liquefiable layer will largely undergo volumetric reconsolidation that can be estimated using 1D procedures
Shallow foundation with shallow liquefiable layer can undergo largely shear-induced movements that cannot be estimated using available 1D procedures
Effective stress analyses based on good earthquake & soil characterization can provide useful insights
RECOMMENDATIONS For earth structures and sloping or free-face ground:
Key issue is are there materials that will lose significant strength as a result of earthquake shaking
Evaluate post-liquefaction residual strength of liquefied soils and calculate FS to investigate flow slide potential
Employ effective mitigation measures, if required
Effective stress analyses based on good earthquake & soil characterization can provide useful insights
Assess earth structure and in situ ground as a system (e.g., void redistribution and thin water films)
Boulanger, R.W., and Idriss, I.M., Closure to Liquefaction Susceptibility Criteria for Silts and Clays, J. of Geotechnical and Geoenvironmental Engineering, ASCE, Vol. 134, No. 7, July, 2008, pp. 1027-1028.
Bray, J.D. and Sancio, R.B., Assessment of the Liquefaction Susceptibility of Fine-Grained Soils, J. of Geotechnical and Geoenvironmental Engineering, ASCE, Vol. 132, No. 9, Sept., 2006, pp. 1165-1177.
Bray, J.D. and Sancio, R.B., Closure to Assessment of the Liquefaction Susceptibility of Fine-Grained Soils, J. of Geotechnical and Geoenvironmental Engineering, ASCE, Vol. 134, No. 7, July, 2008, pp. 1031-1034.
Bray, J.D. and Sancio, R.B., Performance of Buildings in Adapazari during the 1999 Kocaeli, Turkey Earthquake, in Earthquake Geotechnical Case Histories for Performance Based Design, Kokusho, T, Ed., TC4 Committee, ISSMFE, CRC Press/Balkema,The Netherlands, pp. 325-340 & Data on CD-ROM, 2009.
Donahue, J.L., Bray, J.D., and Reimer, M.F. Liquefaction Testing of Fine-Grained Soil Prepared Using Slurry Deposition, Proc. 4th Inter. Conf. Earthquake Geotechnical Engineering, Paper No. 1226, June 25-28, 2007.
Idriss, I.M, and Boulanger, R.S. Soil Liquefaction During Earthquakes. Earthquake Engineering Research Institute, EERIMNO-12, Oakland, CA, 2008.
Sancio, R.B. and Bray, J.D., An Assessment of the Effect of Rod Length on SPT Energy Calculations Based on Measured Field Data, Geotechnical Testing Journal, ASTM, Vol. 28(1), Paper GTJ11959, pp. 1-9, Jan. 2005.
Seed, R.B., Cetin, K.O., Moss, R.E.S., Kammerer, A.M., Wu, J., Pestana, J.M., Riemer, M.F., Sancio, R.B., Bray, J.D., Kayen, R.E., and Faris, A. Recent Advances in Soil Liquefaction Engineering: A Unified and Consistent Framework, 26th Annual ASCE Los Angeles Geotechnical Spring Seminar, Keynote Presentation, Long Beach, Calif., April 30, 2003.
References
Soil LiquefactionOUTLINELIQUEFACTIONLower San Fernando Dam- 1971 San Fernando EQLower San Fernando Dam- 1971 San Fernando EQSlide Number 6LIQUEFACTION Factor of Safety (FS)Post-Liquefaction Residual StrengthSlide Number 10Slide Number 11Slide Number 12Slide Number 13Slide Number 14Slide Number 15Slide Number 16Slide Number 17Slide Number 18Slide Number 20Slide Number 21Slide Number 22Slide Number 23Slide Number 24Slide Number 25Slide Number 26Slide Number 27Slide Number 28Slide Number 29Slide Number 30Evaluation of Ic > 2.6 Criterion Canterbury EQs: Widespread LiquefactionLiquefaction Effects in Christchurch Repeated Liquefaction EventsCTUC BuildingLiquefaction-Induced Differential Settlement Induces DistressCTUC Building: Christchurch EQCTUC Building SettlementSA BuildingLiquefaction-Induced Differential Settlement Induces DistressSlide Number 39SA Building: Sensitivity of ResultsPWC BuildingLiquefaction-Induced Differential Settlement and TiltPWC BuildingSlide Number 43Slide Number 44Slide Number 45Slide Number 46Slide Number 47Slide Number 48