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2013 Ralph B. Peck Lecture
Liquefaction Effects on Structures
Jonathan D. Bray, Ph.D., P.E. Faculty Chair in Earthquake Engineering Excellence
University of California, Berkeley
with S. Dashti, M. Cubrinovski, R. Sancio, J. Zupan, J. Donahue, T. Durgunoglu, P. Byrne, M. Riemer, T. O’Rourke, L. Youd,
J. Pestana, R. Seed, & Others
Primary Sponsor: National Science Foundation
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FOUNDATION ENGINEERINGPeck, Hanson, & Thornburn 1974
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PEOPLE OF SOIL MECHANICS(from Peck, Hanson, & Thornburn 1974)
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GRADUATE STUDENTS(responsible for most of the work)
University of California, Berkeley
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OUTLINE Problem
1999 Kocaeli, Turkey EQ
Field Observations
Experiments: Cyclic Testing & Centrifuge Studies
Analyses
2010-2011 Canterbury, New Zealand EQs
Field Observations
Analyses
Recommendations
Liquefaction Effects on Structures
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PROBLEM: Estimate Liquefaction-Induced Building Movements
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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
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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
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Liquefaction-Induced Building MovementsMarch 11, 2011 Tohoku, Japan Earthquake (Mw = 9.0)
Tokimatsu et al. & GEER ( Ashford et al. 2011)
30 cm 70 cm = 30 cm + 40 cm
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Liquefaction-Induced Building Movements(Previous Work)
Liu
and
Dob
ry, 1
997
Settle
ment
Liq
uefie
d La
yer
Thick
ness
Foundation Width Liquefied Layer Thickness
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LIQUEFACTION
1964 Niigata, Japan EQ (from H.B. Seed)1906 San Francisco EQ (Lawson et al. 1908)
1989 Loma Prieta EQ
EFFECTS
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LIQUEFACTION EFFECTS
Flow Liquefaction Cyclic Mobility(strain-softening large strain) (strain-hardening limited strain)
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LIQUEFACTION Factor of Safety (FS)
Youd et al. 2001 based on Seed et al. 1985
CRR
LiquefactionEffects Observed at Ground Surface No Liquefaction
Effects Observed at Ground Surface
FS = CRR / CSRCSR
FS =1.2
FS =1.2
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LIQUEFACTION EFFECTS
Idriss & Boulanger 2008
Flow Liquefaction
Cyclic Mobility
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Liquefaction Flow Slides when (N1)60 < 15
Idriss & Boulanger 2008
15
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1999 Kocaeli EQ (Mw = 7.5): AdapazariFIELD OBSERVATIONS OF LIQUEFACTION EFFECTS
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Buildings Displace Relative to Surrounding Ground
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Adapazari
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0
1
2
3
2.6 2.8 3.0 3.2 3.4 3.6 3.8 4.0 4.2Distance (km)
Gro
und
Failu
re In
dex
West East
0
1
2
3
4
5S
truct
ural
Dam
age
Inde
x
West East
1 Story
2 Stories
3 Stories
4 Stories
5 Stories
6 Stories
Damage Distribution along Line 1(60 Structures)
Bray & Stewart 2000
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166 CPT/SCPTu & 61 BORINGS with SPT
< http://peer.berkeley.edu/turkey/adapazari >
Fieldwork in Adapazari (Bray et al. 2004)
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Accelerometers
Strain Gages
)()( tAEtF dttAtV )()(
ftt
t
dttVtFEFV0
)()(
6060
EFVNN
Measured Force and Velocity
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0
5
10
15
40 50 60 70 80Energy Ratio (%)
Rod
Len
gth
(m)
0
5
10
15
40 50 60 70 80Energy Ratio (%)
Rod
Len
gth
(m)
N-value = 4 N-value = 10
Correction factors
(Skempton, 1986)
Correction factors
(Skempton, 1986)
SPT Short-Rod Correction
Sancio & Bray 2005
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FillML
CH/CL with some ML/SM layers
SM/ML
CLML CH CH
FillFillFill
CH/CL with some ML/SM layers
CH/CL with some ML/SM layers
Dense SP Dense SP
Dense SP
CL/ML
ML/CL
Generalized Soil Profiles of AdapazariType 1
Liq / LiqType 2
Liq / No LiqType 3
No Liq / LiqType 4No Liq
Sancio et al. 2002
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0
1
2
3
2.6 2.8 3.0 3.2 3.4 3.6 3.8 4.0 4.2Distance (km)
Gro
und
Failu
re In
dex
West East
0
1
2
3
4
5S
truct
ural
Dam
age
Inde
x
West East
1 Story
2 Stories
3 Stories
4 Stories
5 Stories
6 Stories
Damage Distribution along Line 1(60 Structures)
Type 3 Type 4 Type 1(Not Liq. / Liquefiable) (Not Liquefiable) (Liquefiable / Liq.)
Sancio et al. 2002
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Building Response in Adapazari - 1999 Kocaeli EQ
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SITE C - Generalized Subsurface ProfileD
epth
(m
)
“Ground Failure & Building Damage” “No Ground Failure”
Photos by Idriss
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0
1
2
3
4
5
0 20 40 60 80 100
Material Finer than 5 µm (%)
150
1
2
3
4
5
20 40 60 80
Natural Moisture Content and Liquid Limit (%)
Dep
th (m
)
wcLL
PL
35Material Finer than 5µm (%)Natural Moisture Content and Liquid Limit (%)
SITE C: Soil Index Properties
Chinese Criteria (Youd et al. 2001): Liquefaction can only occur if:
1) LL < 35 %, 2) wn > 0.9 LL, and 3) Material Finer than 5 m < 15%
Liquefied Layer
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CKC Automated Triaxial Testing System
Cyclic Triaxial TestingBray & Sancio 2006
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D&M Thin- Walled Piston Sampler
“Undisturbed” Soil Sampling & Testing
Careful Handling
Cut Extrude Test
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0 10 20 30 40 50 60p' (kPa)
-40
-20
0
20
40
-0.5 0.0 0.5Axial Strain (%)
q (k
Pa)
PI = 26 A6 - P8A (e =1.15) LL = 55 ’m = 50 kPa CSR = 0.30 f = 1 Hz FC = 99%
-40
-30
-20
-10
0
10
20
30
40
-6 -4 -2 0 2 4 6
Axial Strain (%)
Dev
iato
r Stre
ss (k
Pa)
-20
-15
-10
-5
0
5
10
15
20
0 10 20 30 40 50
p' (kPa)
q (k
Pa)
PI = 0 F7 - P3A (e =0.74) LL = 27 ’m = 40 kPa CSR = 0.50 f = 0.005 Hz FC = 77%
Bray & Sancio 2006
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-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-P3ALL = 27PI = 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-P2ALL = 25PI = 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-P10ALL = 44PI = 18e = 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-P6ALL = 38PI = 11e = 0.94
cycle 15
cycle 1
Bray & Sancio 2006
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Reconstituted
Soil Specimens
CSS Testing:
Soil G has PI = 10
PI = 2 PI = 5
PI = 11
PI = 14 PI = 7
Donahue et al. 2007
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Cyclic Resistance: PI = 2 & PI = 10 Soils
Slurry Deposition CSS Testing ’v ≈ 137 kPa Donahue et al. 2007
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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 SusceptibleChinese Criteria
(Seed and Idriss 1982
in Youd et al. 2001)
Results of Cyclic Tests
PI & wc/LL Criteria(Bray & Sancio 2006)
Susceptible:
PI 12 & wc/LL ≥ 0.85
Moderate Susceptibility:
wc/LL > 0.8 & 12 < PI 200
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
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Evaluation of Ic > 2.6 Criterion
A liquefaction site in Adapazari (Bray & Sancio 2009)
2.6 12 0.85
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Cyclic Mobility Susceptibility of Fine-Grained Soils
1. % clay-size criterion is unreliable: Do not use Chinese Criteria
2. Focus on soil mineralogy & sensitivity: - Soils with PI ≤ 12 & wc/LL ≥ 0.85 can undergo cyclic mobility- Other soils can undergo severe strength loss
3. Use cyclic testing on “undisturbed” specimens
4. Cyclic response of silty soils depends on:
- Void ratio - Stress history- Time under confinement- Loading frequency- Specimen preparation method- Testing device
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Centrifuge ExperimentsDashti et al. 2010a & 2010b using NEES @ Davis
Use centrifuge testing to evaluate:
• Effects of thin liquefiable layers• Mechanisms of liquefaction-induced ground settlement• Consequences of liquefaction on building performance• Potential mitigation measures
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Centrifuge Tests: Soil Profile
Dense Nevada SandDr ≈ 85 - 90%
3 m to 6 mLoose Nevada SandDr = 30% – 50%
Dense Monterey Sand 2 m
18 m to 21 m
Test
Layer Thick-ness/ Dr
T6-30 6 m / 30%
T3-30 3 m / 30%
T3-50SILT
3 m / 50%
T3-50 3 m / 50%
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Under Structure A
-60
-30
0
30
60
90
120
150
0 5 10 15 20 25 30 35 40 45 50
time (sec)
exce
ss p
ore
pres
sure
(k
Pa)
SHD02
SHD03
Ru = 1.0
Adjacent to Structure A
-60
-30
0
30
60
90
120
150
0 5 10 15 20 25 30 35 40 45 50
time (sec)
exce
ss p
ore
pres
sure
(k
Pa)
SHD02
SHD03
Ru = 1.0
Free Field
-60-30
0306090
120150
0 5 10 15 20 25 30 35 40 45 50
time (sec)
exce
ss p
ore
pres
sure
(k
Pa)
SHD02
SHD03
Ru = 1.0
Pore Water Pressure Response Near Buildings(3 m thick liquefiable layer; SHD02: Dr = 30% & SHD03: Dr = 50%)
A B C
A
B
C
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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
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DISPLACEMENT MECHANISMS1. Volumetric Deformations
Partial Drainage (εp-DR)
Sedimentation (εp-SED)
Consolidation (εp-CON)
2. Shear-Induced Deformations
Bearing Capacity Failure (εq-BC)
SSI-Induced Ratcheting (εq-SSI)
3. Ground Loss due to Ejecta
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Dashti et al. 2010a
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Dashti et al. 2010a
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PGA = 0.15 g
D5-95 (s) = 8 s
Ia = 0.3 m/s
PGA = 0.13 g
D5-95 (s) = 28 s
Ia = 0.6 m/s
PGA = 0.38 g
D5-95 (s) = 11 s
Ia = 2.7 m/s
Effects of Ground MotionDashti et al. 2010b
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Shaking Intensity Rate = SIR = Ia5-75 / D5-75
Effects of Ground MotionDashti et al. 2010b
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Isolation of Key Mechanisms &Effects of Potential Mitigation Techniques
SW - Structural Wall
BL - Baseline
WB – Water Barrier
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Liquefaction Mechanisms and MitigationS
truc. BL
(Baseline)
Struc. W
B
(Water B
arrier)S
truc. SW
(S
tructural Wall)
Vert
ical
Dis
plac
emen
t (m
m)
Arias Intensity (cm
/s)
-20
0
20
40
60
80
100
1200 10 20 30 40 50
-7
0
7
14
21
28
35
Struc. WB
Struc. BL
Struc. SW
Arias Intensity
Moderate Port Island
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Calculated Shear Strain & Volumetric Strain
Maximum Shear Strain
Volumetric Strain
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
Shea
r Str
ain
(%)
Time (sec)
Nevada Sand CSS testsArulmoli et al. 1992 Dr = 63%, CSR = 0.3, K = 0
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Measured vs. Calculated Responses
Centrifuge experiment T3-50 during the moderate Port Island event
0 10 20 30 40
0
50
100
150
200
Centrifuge
Ver
tical
Dis
plac
emen
t (m
m)
Base Acceleration
Structure BL Displacement
0 10 20 30 40
-0.500.5
0 10 20 30 400
20
40
60
Exc
ess
Por
e P
ress
ure
(kP
a)
Time (sec)
Position within liquef. layer:
Top
Middle
Bottom
0 10 20 30 40
0
50
100
150
200
FLAC Simulation
Base Acceleration
Structure BL Displacement
0 10 20 30 40
-0.500.5
Acceleration (g)
0 10 20 30 400
20
40
60
Time (sec)
Position within liquef. layer:
Top
MiddleBottom
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Calculated vs. Measured Settlement
Cal
cula
ted
Sett
lem
ent (
mm
)
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CENTRIFUGE TEST FINDINGSBuilding settlements are not proportional to the thickness of the liquefiable layer
Free-field settlements result from volumetric strains
Building movements result from shear strains and volumetric strains & loss of ground with ejecta
Building settlement is related to shaking intensity rate and relative density of soil
These observations are not captured in available simplified methods that focus on free-field reconsolidation settlement
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• Large amounts of sand ejecta
• Significant damage to structures & utilities
Canterbury EQs: Severe Liquefaction
Cubrinovski et al.
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Liquefaction Effects on Structures
15 cm
1.8o
Tilting and Sliding of Buildings Settlement of Ground next to Piled Bldg.
30 cm
= 1/70
Cracking due to Differential Settlement Uniform Settlement of Building
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Liquefaction from 3+ EQs (Cubrinovski 2011)
Base Map – 22 Feb 2011 – Mw = 6.2White Areas – 4 Sep 2010 – Mw = 7.1Black Areas – 13 Jun 2011 – Mw = 6.0
CBD
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Seismic Demand from Recent EQsEvent Median PGA (g)
Magnitude Scaling Factor
(Idriss & Boulanger 2008)
MedianCSRM7.5
(16% - 84%)
Level of Liquefaction
in CBDCBGS CCCC CHHC REHS
4 SEP 10Mw = 7.1 0.17 0.21 0.18 0.25 1.1 0.10
(0.10 - 0.17)Low
26 DEC 10Mw = 4.8 0.25 0.22 0.16 0.24 1.8 0.07 None
22 FEB 11Mw = 6.2 0.48 0.42 0.35 0.51 1.4 0.20
(0.16 - 0.28)Severe
13 JUN 11Mw = 6.0 0.16 - 0.21 0.29 1.5 0.09
(0.08 – 0.15)Low
23 DEC 11Mw = 5.9 0.20 0.18 0.21 0.30 1.5 0.10 Low
CSRM7.5 = 0.65 (PGA/g) / MSF MSF = 6.9 exp(-Mw/4) – 0.058 ≤ 1.8
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Central Business District of ChristchurchStrong Motion Station
UCB/UC Study Zones
Liquefaction22 FEB 2011
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Streams in Central Christchurch (from 1850’s ‘Black Maps’)
from M. Cubrinovski
Armaph St.
Mad
ras
St.
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CTUC BuildingLiquefaction-Induced Differential Settlement Induces Distress
GEER: Bray, Cubrinovski et al.
Building Settlement (cm)Maximum Angular Distortion ≈ 1 / 50
490
7811206
31
Ejecta
0
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CTUC Building: Christchurch EQ
2011 Christchurch EQ: Robertson & Wride (1998)
N
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CTUC Building Settlement
~40 cm ~15 cm
Actual Settlement
~15 cm ~10 cm ~5 cm
Robertson & Wride (1998) & Zhang, Robertson et al. (2002)
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0 0.5 1 1.5 2
0
1
2
3
4
5
6
7
8
9
10
FS
Dep
th (m
)
0 5 10 15 20
0
1
2
3
4
5
6
7
8
9
10
Settlement (cm)
4 SEP 1026 DEC 1022 FEB 1113 JUN 11
CTUC Building: Sensitivity of Results
Robertson & Wride (1998) & Zhang, Robertson et al. (2002)
CPT Z4-5
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PWC BuildingLiquefaction-Induced Differential Settlement and Tilt
GEER: Bray, Cubrinovski et l
21 stories on basement mat
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PWC Building
2011 Christchurch EQ: Robertson & Wride (1998)
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Canterbury EQs Findings• Liquefaction severely damaged buildings,
and utilities in the Central Business District
• Each EQ was well recorded, so there is an opportunity to refine analytical procedures
• Loose shallow silty sand layer, when present, led to much of the damage in the CBD, especially in areas of significant ejecta
• Current analytical procedures predict liquefaction triggering well but not its effects
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CONCLUSIONS• Effects of liquefaction can be severe
• Cyclic mobility occurs for PI ≤ 12 & wc/LL ≥ 0.85 soil
• Shallow, loose sands & silts led to much of the damage, especially when ejecta occurred
• 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 structures with shallow foundations
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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
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RECOMMENDATIONSFor 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 cannotbe estimated using available 1D procedures
Effective stress analyses based on good earthquake & soil characterization can provide useful insights