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

FOUNDATION ENGINEERINGPeck, Hanson, & Thornburn 1974

PEOPLE OF SOIL MECHANICS(from Peck, Hanson, & Thornburn 1974)

GRADUATE STUDENTS(responsible for most of the work)

University of California, Berkeley

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

PROBLEM: Estimate Liquefaction-Induced Building Movements

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

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

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

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

LIQUEFACTION

1964 Niigata, Japan EQ (from H.B. Seed)1906 San Francisco EQ (Lawson et al. 1908)

1989 Loma Prieta EQ

EFFECTS

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

LiquefactionEffects Observed at Ground Surface No Liquefaction

Effects Observed at Ground Surface

FS = CRR / CSRCSR

FS =1.2

FS =1.2

LIQUEFACTION EFFECTS

Idriss & Boulanger 2008

Flow Liquefaction

Cyclic Mobility

Liquefaction Flow Slides when (N1)60 < 15

Idriss & Boulanger 2008

15

1999 Kocaeli EQ (Mw = 7.5): AdapazariFIELD OBSERVATIONS OF LIQUEFACTION EFFECTS

Buildings Displace Relative to Surrounding Ground

Adapazari

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

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

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

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

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

Building Response in Adapazari - 1999 Kocaeli EQ

SITE C - Generalized Subsurface ProfileD

epth

(m

)

“Ground Failure & Building Damage” “No Ground Failure”

Photos by Idriss

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

CKC Automated Triaxial Testing System

Cyclic Triaxial TestingBray & Sancio 2006

D&M Thin- Walled Piston Sampler

“Undisturbed” Soil Sampling & Testing

Careful Handling

Cut Extrude Test

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

-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

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 Resistance: PI = 2 & PI = 10 Soils

Slurry Deposition CSS Testing ’v ≈ 137 kPa Donahue et al. 2007

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

Evaluation of Ic > 2.6 Criterion

A liquefaction site in Adapazari (Bray & Sancio 2009)

2.6 12 0.85

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

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

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%

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

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

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

Dashti et al. 2010a

Dashti et al. 2010a

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

Shaking Intensity Rate = SIR = Ia5-75 / D5-75

Effects of Ground MotionDashti et al. 2010b

Isolation of Key Mechanisms &Effects of Potential Mitigation Techniques

SW - Structural Wall

BL - Baseline

WB – Water Barrier

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

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

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

Calculated vs. Measured Settlement

Cal

cula

ted

Sett

lem

ent (

mm

)

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

• Large amounts of sand ejecta

• Significant damage to structures & utilities

Canterbury EQs: Severe Liquefaction

Cubrinovski et al.

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

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

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

Central Business District of ChristchurchStrong Motion Station

UCB/UC Study Zones

Liquefaction22 FEB 2011

Streams in Central Christchurch (from 1850’s ‘Black Maps’)

from M. Cubrinovski

Armaph St.

Mad

ras

St.

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

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)

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

PWC BuildingLiquefaction-Induced Differential Settlement and Tilt

GEER: Bray, Cubrinovski et l

21 stories on basement mat

PWC Building

2011 Christchurch EQ: Robertson & Wride (1998)

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

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

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

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