1

UPDATE OF THE SPT- AND CPT-BASED LIQUEFACTION TRIGGERING PROCEDURES

presented by

I. M. IdrissProfessor Emeritus, University of California at Davis

Consulting Geotechnical Engineer, Santa Fe, NMimidriss@aol.com

Presented at the

1st WORKSHOP ON GEOTECHNICAL EARTHQUAKE ENGINEERING

"Liquefaction Evaluation, Mapping, Simulation and Mitigation"

Organized by

Earthquake Engineering Research Institute (EERI) San Diego Chapter

San DiegoSeptember 12, 2014

Reference material

The presentation today is based on material published in the following report:

Boulanger, R. W. and Idriss, I. M. (2014) "CPT and SPT Based Liquefaction Triggering Procedures", ReportUCD/CGM- 14/01, Department of Civil and Environmental Engineering, University of California, Davis, CA, 138 pp.

This report can be downloaded from:

http://retrocee.engr.ucdavis.edu/faculty/boulanger/PDFs/2014/Boulanger_Idriss_CPT_and_SPT_Liq_triggering_CGM‐14‐01_2014.pdf

2

Outline of Presentation

1. Magnitude Scaling Factor (MSF)

Modified MSF expression to be a function of magnitude, soil type, and denseness of the soil

2. Update of SPT-based approach

Added 24 Case Histories (14 from Turkey & 10 from Taiwan)

Incorporated new MSF expression

No change in CRR versus (N1)60cs

3

Outline of Presentation

3. Update of CPT-based approach

Changed qc1N as a function of FC

Changed CRR versus qc1Ncs

4. Examination of the CPT-based case histories in terms of the soil behavior type (SBT) index, IC

MAGNITUDE SCALING FACTOR (MSF)

4

DEMAND -- CSR

The value of CSR for each case history is calculated usingthe following expression:

v

vo maxdM 7.5 ; ' 1 atm

vo

a 1 1CSR 0.65 r

' KMSF

Acc

eler

atio

n

Time

Acc

ele

rati

on

Time

Acc

eler

atio

n

Time

Effects of duration

M = 5.1

M = 6.5

M = 7.3

5

History of the development of MSF:

1. Seed et al. (1975): proposed a relationship between "Number of Equivalent Uniform Cycles, Neq" & Magnitude, M, which led to the initial development of "MSF Values".

2. Seed & Idriss (1982): Tabulated "MSF Values" as a function of M; used shaking table test results by DeAlba et al. (1976) relating CRR to "Number of Uniform Cycles".

3. Idriss (1999): Used results of cyclic tests on frozen samples by Yoshimi et al. (1984) to derive a revised relationship between Neq & M, which resulted in a revised MSF relationship.

4. Boulanger & Idriss (2014): Modified MSF expression to be a function of magnitude, soil type, and denseness of the soil, as summarized in this presentation.

MSF used to account of effects of duration

Cyclic Stress Ratios Used in Re-Deriving EquivalentUniform Cycles as a Function of Earthquake Magnitude

Number of Cycles, N

1 10 100

Cyc

lic

Str

ess

Rat

io

0.04

0.06

0.08

0.2

0.4

0.6

0.8

2

0.1

1 Test results by Yoshimi et al (1984)on frozen samples

Test results by Yoshimi et al (1984)on tube samples

Test results by DeAlba et al (1976) normalizedto a relative density = 68% at 10 Cycles

(see Fig. 3 re: Legend for individual test series)

bCRR aN

6

Number of Cycles Required t o Cause 5 % D.A. St rain

1 10 10 0

Cy

clic

St

res

s R

at

io ( d

/2 o

') a

t N

um

be

r o

f C

yc

les

= N

Cy

clic

St

res

s R

at

io ( d

/2 o

') a

t N

um

be

r o

f C

yc

les

= 1

5 c

ycl

es

0 .2

0 .3

0 .4

0 .6

0 .8

2

3

0 .1

1

Based on Test Result s byYoshimi et al (19 8 4 )

Based onTest Result s by DeAlba et al (19 76 )

Normalized t o a Relat ive Densit y = 6 8 %

Normalized Cyclic Stress Ratios Used in Re-DerivingEquivalent Uniform Cycles as a Function of Earthquake Magnitude

Earthquake Magnitude, M

4 5 6 7 8 9

Nu

mb

er o

f E

qu

ival

ent

Str

ess

Cyc

les

0

10

20

30

40Seed & Idriss (1982)Idriss (1999)

Figure 62 – Mean number of equivalent uniform cycles at 65% of the peak stress versus earthquake magnitude.

Effects of duration

7

Figure 62 – Mean number of equivalent uniform cycles at 65% of the peak stress versus earthquake magnitude.

Effects of duration

Earthquake Magnitude, M

4 5 6 7 8 9

Nu

mb

er o

f E

qu

ival

ent

Str

ess

Cyc

les

0

10

20

30

40Seed & Idriss (1982)Idriss (1999)

Effects of duration

The number of cycles representing a given magnitude from theprevious figure can be used in the lab-generated CSR versus Nplot to obtain the level of CSR corresponding to that magnitude.This value of CSR divided by the CSR for a reference magnitude(usually M = 7½) is defined as a "magnitude scaling factor orMSF".

MSF is then used as a proxy for duration and is expressed as afunction of earthquake magnitude.

8

Effects of duration

Number of Cycles, N

1 10 100

CR

R

0.0

0.1

0.2

0.3

0.4Test results by DeAlba et al (1976) normalized

to a relative density = 68% at 10 Cycles(see Fig. 19 re: Legend for individual test series)

Magnitude = 7.515 cycles

Effects of duration

Number of Cycles, N

1 10 100

CR

R

0.0

0.1

0.2

0.3

0.4Test results by DeAlba et al (1976) normalized

to a relative density = 68% at 10 Cycles(see Fig. 19 re: Legend for individual test series)

Magnitude = 6.56.8 cycles

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Number of Cycles Required to Reach ru = 100% or 5% DA Strain

1 10 100

CR

R a

t N

Cyc

les

/ CR

R a

t N

= 1

5

0.0

0.5

1.0

1.5

2.0

2.5

Ma

gn

itu

de

= 5

½

Ma

gn

itu

de

= 6

½

Mag

nit

ud

e =

7½

Ma

gn

itu

de

= 8

½

1.69

1.30

1.00

0.77

MSF

Illustration of the variation of MSF with number of cycles and magnitude.

Magnitude scaling factor values proposed by various investigators

Earthquake moment magnitude, M

5 6 7 8 9

Mag

nit

ud

e sc

alin

g f

acto

r, M

SF

0

1

2

3

Seed & Idriss (1982)

Ambraseys (1985)

Arango (1996)

Idriss (1999)

Tokimatsu & Yoshimi (1983)

Cetin et al (2004)

MMSF 6.9exp 0.058

4

10

MSF relationship for clays and plastic silts (Boulanger and Idriss 2007)

0.1 1 10 100

Number of Cycles, N, to reach 5% D.A. strain

0.1

1

0.2

0.4

0.6

0.8

2

0.08

0.06

0.04

Cy

clic

Str

ess

Rat

io C

SR

=

d /

2'

o

Yoshimi et al (1984):Cyclic TX on frozen samples

of dense Niigata sand

Silver et al. (1976):Cyclic TX on moist tampedMonterey sand ( DR=60% )

Toki et al. (1986):Cyclic TX on air pluviatedToyoura sand ( DR=50% )

b = 0.22

b = 0.10

b = 0.34

Effects of denseness on slope b

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5 6 7 8 9Earthquake magnitude, Mw

0

1

2

3

0.40

0.34

0.280.220.16

b =

Variation in the MSF relationship with parameter b

Variation in the MSF relationship with (N1)60cs & qc1Ncs

5 6 7 8 9Earthquake magnitude, Mw

0

0.5

1

1.5

2

2.5

(N1)60cs=30, qc1Ncs=175

(N1)60cs=20, qc1Ncs=133

(N1)60cs=10, qc1Ncs=84

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UPDATE OF THE CPT-BASED APPROACH

Total number of CPT-based

case histories: 253Y/N/M 180/71/2

US case histories:Y/N/M 65/35/1

Japan case histories:Y/N/M 24/13/1

New Zealand case histories:Y/N 53/16

Other case histories:Y/N 38/7

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DEMAND – CSR

The value of CSR for each case history is calculated usingthe following expression:

v

vo max dM 7.5 ; ' 1 atm

vo

a r 1CSR 0.65

' MSF K

Key expressions – CPT-based procedure

m

aN

v

0.264

c1N

PC 1.7

m 1.338 0.249 q

c1 N cq C q

c1N c1 aq q P

Pa = atmospheric pressure having same units as qc

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Key expressions – CPT-based procedure

n

c v a'

a v

q PQ

P

s

c v

fF .100

q

2 2

C 10 10I 3.47 Log Q 1.22 Log F

C FC

FC

FC 80 I C 137

C 0, -0.29, 0.29

c1N ,cs c1N c1Nq q q

15

qc1Ncs

0 50 100 150 200 250

CS

RM

=7.

5,'

v=

1at

m

0.0

0.1

0.2

0.3

0.4

0.5

0.6

CPT data based on 2014 interpretation Process

Liq. No Liq. MarginalUSA

Japan

New Zealand

Others

Triggering relationship(Boulanger & Idriss, 2014)

Triggering relationship(Idriss & Boulanger, 2008)

De

pth

of

crit

ical

zo

ne

(m

)D

ep

th o

f cr

itic

al z

on

e (

m)

16

17

Soil Behavior Type (SBT) Index, IC

State Parameter,

CPT-based soil behavior type classification chart by Robertson (1990)

18

Liquefaction failure case histories (from Robertson 2010)State parameter, = -0.05

= -0.05

Normalized friction ratio, F (%)

0.1 1 10

No

rmal

ize

d c

on

e ti

p r

es

ista

nc

e,

Q

1

10

100

10001.4 < Ic < 1.64 [9]

1.64 < Ic < 2 [80]

2.0 < Ic < 2.2 [49]

2.2 < Ic < 2.4 [29]

2.4 < Ic < 2.6 [13]

CPT LiquefactionCase Histories

19

Normalized friction ratio, F (%)

0.1 1 10

No

rmal

ized

co

ne

tip

res

ista

nce

, Q

1

10

100

1000

State parameter = -0.05

1.4 < Ic < 1.64 [9]

1.64 < Ic < 2 [80]

2.0 < Ic < 2.2 [49]

2.2 < Ic < 2.4 [29]

2.4 < Ic < 2.6 [13]

CPT LiquefactionCase Histories

Normalized friction ratio, F (%)

0.1 1 10

No

rmal

ized

co

ne

tip

res

ista

nce

, Q

1

10

100

1000

State parameter = -0.05

1.4 < Ic < 1.64 [21]

1.64 < Ic < 2 [28]

2.0 < Ic < 2.2 [12]

2.2 < Ic < 2.4 [5]

2.4 < Ic < 2.6 [5]

CPT No LiquefactionCase Histories

20

The Cone Penetration Test (CPT) has proven to be a veryvaluable tool for characterizing subsurface conditions andassessing various soil properties, including estimating thepotential for liquefaction.

The main advantages of using the CPT are that it provides acontinuous record of the penetration resistance and is lessvulnerable to operator error than is the SPT test.

Its main disadvantages are the difficulty in penetrating throughlayers with larger particles (e.g., gravels) or very highpenetration resistances (e.g., strongly cemented soils) and theneed to perform companion borings or soundings to obtain soilsamples.

Concluding remarks

Development of the CRR versus (N1)60cs or qc1Ncs relations arebased on using the equation:

Therefore, "forward" calculations should also be based onusing this equation.

Calculation of shear stresses by convolving an inadequatenumber of input rock motions can lead to serious over orunder estimation. The minimum number of input rockmotions appears to be 7, but this issue is still underinvestigation.

vo max dM 7.5

vo

a r 1CRR 0.65

' MSF K

Concluding remarks

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Elements that affect site response in order of importance:

Input MotionSoil ProfileSoil PropertiesMethod of Analysis

Concluding remarks

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