Proceedings of the International Symposium on Engineering Lessons Learned fromthe 2011 Great East Japan Earthquake, March 1-4, 2012, Tokyo, Japan

EFFECTIVE STRESS ANALYSES OF TWO SITESWITH DIFFERENT EXTENT OF LIQUEFACTION
DURING EAST JAPAN EARTHQUAKE
Hideki FUNAHARA1, Sadayuki ISHIZAKI2 and Toshiaki NAGAO3
1Senior Research Engineer, Technology Center, Taisei Corporation, Yokohama, Japan,hideki.funahara@sakura.taisei.co.jp
2
Research Engineer, Technology Center, Taisei Corporation, Yokohama, Japan,sada.ishizaki@sakura.taisei.co.jp
3
Chief Research Engineer, Technology Center, Taisei Corporation, Yokohama, Japan,toshiaki.nagao@sakura.taisei.co.jp

ABSTRACT: The liquefaction extent observed along the Tokyo bay coast during theGreat East Japan earthquake drastically differed depending on its location. Two locations
in reclaimed areas, which have similar soil profiles, showed different liquefaction extent(i.e. One location heavily liquefied and another did not.). In this study, we employed adynamic effective stress analysis technique to simulate the difference of the seismic
behaviors of the two sites. The simulation implies a possibility that the liquefaction
resistance at large cyclic numbers could affect the liquefaction occurrence due to therelatively small but long input motion.
Key Words: Great East Japan earthquake, liquefaction, effective stress analysis,
reclaimed area of Tokyo bay coast, long duration of seismic motion

INTRODUCTION
The soil liquefaction was widely observed during the Great East Japan earthquake. Especially theliquefaction along the Tokyo bay coast received a lot of attention because the distances from theepicenter were long and the seismic intensities around the liquefied locations were relatively small. It
is pointed out that the long duration of the seismic motion due to the large magnitude of theearthquake could be an important factor of the heavy liquefaction occurrence.
On the other hand, the liquefaction extent differed depending on the locations in reclaimed areas.
The factors that affected the liquefaction extent could be the grain size distributions of the soil, thereclamation histories, the soil structure below the reclaimed layers and/or soil improvement works.
However, the whole picture is not still understood precisely.
In this study, we look at two locations that showed different behaviors from the viewpoint ofliquefaction occurrence. In order to estimate the seismic behaviors of the ground like pore waterpressures, we conducted dynamic analyses using an effective stress analysis program. The focusedfactors are the modeling of the liquefaction strength curve and the small but long input motion.

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OUTLINE OF THE TWO LOCATIONS
The first location (Site A) is Shin-Kiba, Koto ward and the second location (Site B) is Rinkai-cho,
Edogawa ward. As shown in Figure 1, the two sites are in reclaimed areas around the Arakawa rivermouth and located on opposite sides. The distance between the two sites is about 2 km.
The ground at site A heavily liquefied and many sand boils were observed (Photo 1). Many smallbuildings such as one or two-story offices, which probably sit on shallow foundations, suffereddifferential settlements. On the other hand, no liquefaction and no structural damage were observed
around site B.

Fig. 1 Locations of the two sites studied in this research (Google maps)

Photo 1 Sand boils observed in Shin-Kiba area
Figure 2 shows the geological logs, the SPT-N values and PS logs of site A and B. The soil
profiles consist of the upper landfill layer, loose alluvial sandy layer (upper Yurakucho layer,
10-14 m thickness), soft alluvial clayey layer (lower Yurakucho layer, about 20 m thickness),and relatively dense alluvial sandy layer (Nanagochi layer, 8 m thickness at site A, 20 m
thickness at site B). The firm diluvial layer that has SPT-N value of more than 50 appears at
the depth of 44 m (site A) and at the depth of 56 m (site B).

802Reclaimed
Soil0

Reclaimed
Soil0

Silty Sand(Sand)
SiltSandSilt

Silt1010Silty
SandSandSandy
SiltSandy
Silt20Depth (m)Depth (m)20

Silt30Clay40

Silt30Clay40

Sand50Sand

60060 0Site A N-Value

200

40050

Clay60

Sand
Sand& Gravel

0Site BVs (m/s)

60 0

N-Value200

400

Vs (m/s)Fig. 2 Geological columns and PS logs
Site A
8.0-8.3m
10.0-10.3m

80
60
40200
Clay-200.001

Silt0.01

Fine Med. Coar.
Sand0.11Grain Size (mm)Gravel10Site B (No.2 GL-13~13.9m)

100
Percentage Passing (%)

Percentage Passing (%)

100

C-9-3-1
C-9-3-2
C-9-3-3
C-9-3-48060
40200Clay

100-200.001

Silt0.01

Fine Med. Coar.
Sand0.1
1Grain Size (mm)Gravel10100Fig. 3 Grain size accumulation curve
The boring logs for the two sites imply the liquefaction susceptibility of the reclaimed
surface layer and the loose alluvial sandy layer. Figure 3 and Table 1 present the grain size

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distribution curves and several characteristics of those liquefiable layers. The characteristicsof the grain size distributions are mostly similar between the two sites, except the differenceof the uniformity coefficient.
The fines contents of most samples exceed 35%, which is the upper limit of theliquefaction susceptible candidate for natural deposits in AIJ recommendations (ArchitecturalInstitute of Japan 2001).
According to several geotechnical surveyors, it is difficult to draw a borderline between a
man-made layer reclaimed by dredging and the underlying natural deposit. Therefore, there
is a possibility that some soil layers that is expressed like natural deposits in Figure 2 might
be reclaimed layers. If this possibility is true, the silt layers could be liquefiable. However, at
this stage, there is not any reliable evidence to change the natural silt to a liquefiable
reclaimed soil. Therefore, in this study, we would assume that the soil less than 50% fines orless than 10% clays could be liquefiable.

Table 1 Characteristics of grain size distributions
Site A

Site B (No.2 GL-13～14m)

8m

10m

1234D50(mm)0.09040.09110.12210.07310.05980.0659

Fc(%)

4441

28.2

50.7

59.9

60.5

Pc(%)

911

1.9

15.3

6.2

4.5

Uc

19.31 26.31
2.78
-7.04
4.84
D50: Average Grain Size, Fc: fine fraction content
Pc: Clay fraction content , Uc: uniformity Coefficient

SIMPLIFIED LIQUEFACTION ASSESSMENT
Based on a method recommended in AIJ recommendations (Architectural Institute ofJapan 2001), simplified liquefaction assessments were conducted. This method utilizes SPT-N
value and fines content to estimate the liquefaction resistance of the ground. The Magnitudeof 9.0 and the ground peak acceleration of 150 cm/s2 are assumed considering the earthquake
records obtained through K-net (http://www.kyoshin.bosai.go.jp/kyoshin/). The layers that
contain more than 50% fines and more than 10% clay are considered as non-liquefiable layers.
00 Reclaimed

Reclaimed
Soil

Soil
Silty
Sand

10155

Not
candidate

Silt

Sandy Silt

Depth (m)Depth (m)

52.29

Silty
SandSilty
Sand

1015Sandy
Silt
Silty
SandSandySilt

Notcandidate

Sandy
Silt

20200Site A1Not
candidate

Silt2FlSite B(No.3)

Not
candidate

01FlFig.4 Computed safety factors against liquefaction

8042

Figure 4 shows the results of liquefaction assessment. The computed safety factors
against liquefaction (Fl) are less than 1.0 at several depths for both sites. In other words, theassessments predict the occurrence of liquefaction for both sites. However, in reality, theliquefaction was not observed at site B.
The cyclic displacement of ground surface (Dcy) can be estimated based on the simplifiedliquefaction assessment, and Dcy implies the extent of liquefaction. The estimated Dcy for site
A is 2.5 cm that means the liquefaction extent is slight. On the other hand, the estimated Dcyfor site B is 7.0 cm that means the liquefaction extent is small. The assessment for site Apredicts the liquefaction occurrence itself. However, considering the amount of sand boils
observed at the site, Dcy for site A could be underestimation.

DYNAMIC EFFECTIVE STRESS ANALYSES
Purpose of the dynamic analyses
The seismic motion during the Great East Japan earthquake continued for long duration. However, thesimplified assessment mentioned above would have limits to be applied to such a long seismic motion.
Therefore, in order to evaluate the dynamic behavior of soil, such as pore water pressure accumulation,
acceleration, deformation etc., we conducted dynamic analyses utilizing an effective stress analysis
program.
Numerical modeling
Outline of the modeling
The employed computation program is 'TDAPIII'. The numerical model is one dimensional soilcolumn that consists of plane strain elements.
Modeling of non-liquefiable soil
The constitutive model for non-liquefiable layers is 'Modified Ramberg-Osgood Model'. Figure 5
presents the employed curves of shear strain dependency of shear stiffness and damping ratio. For siteA, typical relations published in a reference (Architectural Institute of Japan 2006) are used. On
the other hand, for site B, the laboratory testing data was available and targeted for modeling.
1

0.4

0.8

0G/G

0.4

0.2

Cohensive Soil

0.1

0.2
0-6
10

0.6

10-5-4-3

1010
Shear Strain

10-2

010

0.5
0.4

Cohensive Soil（Alluvium）

0.3

Cohesive Soil（Alluvium）

0.4

Sandy Soil(Diluvium)

0.2

0.2

Cohesive SoilDiluvium）

0.10-610-1

Site B

10-5-4-3

1010
Shear Strain

10-2

Damping Facter

Sandy Soil

Damping Facter

0.3

0.600.8

0.5G/G

Site A

1010-1Fig. 5 Models of dynamic deformation characteristics
Modeling of liquefiable soil
The constitutive model for liquefiable layers is 'Stress-Density model' (Cubrinovski 1998a,Cubrinovski 1998b). The important target for modeling of the constitutive model is a liquefaction

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strength curve. Figure 6 presents the liquefaction strength curves of the model. We had liquefaction
testing data only for site B. Therefore, the testing data of site B was used as targets for modeling. On
the other hand, for site A, we employed the parameters determined for Toyoura sand and adjusted thevoid ratio to fit the liquefaction strength at cyclic number of 15 that is computed in the simplified
assessment mentioned above.
The essential difference of the liquefaction strength curves of the models at site A and site B
should be looked at here, because the difference would affect the computed liquefaction behaviors
afterward. The liquefaction strength curve of site A is slightly lower than the curve of site B as a result.
Especially the difference is large at the large cyclic numbers. The modeling of the soil at site A isconducted simply by fitting the liquefaction strength at the cyclic number of 15 and the other cyclic
numbers are not cared. On the other hand, when modeling the soil at site B, the whole averaged shapeof the scattered liquefaction strength data are targeted and the inclination of the liquefaction strength
curve is controlled.

0.4

τl/σ'z orτl/σ'z

0.2

01

Analysis Model
Recommendationof Design
10100
Number of Repeat Countσd/2σ'0×(1+2K0)/30.4

Site A
GL-13.5m
σ'z=125 kPa

Site B
GL-12～14m

0.2
Analysis Model
No.1
No.2Tests
No.4
No.5
No.601
10100
Number of Repeat Count

Fig.6 Models of liquefaction resistance curves
Input motion
As the input acceleration at the engineering bedrock for the dynamic analyses, a seismic record
obtained by Port and Airport Research Institute (PARI) at Ooi-site was used
( http://www.mlit.go.jp/kowan/kyosin/eq.htm ). The location of Ooi is shown in Figure 1. The time
history of the input motion is shown in Figure 7. The maximum acceleration is less than 70 cm/s2 andthe duration is more than 6 minutes.

(cm/s2)

Acc.

80

max=65.9cm/s2, Min=-63.1cm/s20-80
050

100

150

200
250
Time (s)300

Fig.7 Input motion (seismic record: PARI)

806

350

400

Simulated liquefaction behavior of the two locations
Time histories of the ground responses
Figure 8 shows time histories of the accelerations, the ground surface displacement and the excess
pore water pressure ratio.
The excess pore water pressure ratio at the depth of 8.5 m at site A builds up gradually and reaches
almost 1.0 or liquefies after more than 100 seconds. On the other hand, the excess pore water pressure
ratio at site B reaches only 0.5 or does not liquefy.
Regarding the acceleration responses, the input acceleration less than 70 cm/s2 amplifies up toalmost 150 cm/s2 at the ground surface. This is consistent with the seismic record obtained around thesites. At site A, after the liquefaction triggering at around 125 seconds, the amplitude of theacceleration drastically decreases due to liquefaction.
The horizontal displacement at the ground surface after 125 seconds exhibits a longer period
motion for long duration. The elongated period seems around 5 seconds and the double amplitude isalmost 10 cm. Such an elongated period due to liquefaction cannot be seen at site B.
Acc.
(cm/s2)150(a) Ground Surface

0Disp.
(cm)-15020(b) Ground Surface

0P.W.P.R.

-20
1
0.5(c) GL-8.5m

Acc.
(m/s2)

0150(d) GL-16.0m

0-150050

100

150200250Time (s)300350400(a) Site AAcc.
(cm/s2)150(a) Ground Surface

0P.W.P.R.

Disp.
(cm)

-150
20(b) Ground Surface

0-2010.5(c) GL-10.5m

Acc.
(m/s2)

0150(d) GL-16.0m

0-150050100150200250Time (s)300350(a) Site B
Fig. 8 Time histories of responses of soil

807

400

Stress strain relation and effective stress path
Figure 9 shows the shear stress - shear strain relations and the effective stress paths of the effective
stress models for both sites. The effective stress path is the relation between the mean effective stressand shear stress.
Regarding site A, the mean effective stress in the effective stress path reaches almost zero and theshear stiffness in the stress strain relation drastically decreases due to liquefaction. After triggeringliquefaction, the stress-strain relation exhibits some inverse S shaped behaviors. On the other hand, thestress-strain relation of site B does not exhibit such behaviors.
30Site A
GL-8.5m
Shear Stress(kN/m2)

Shear Stress(kN/m2)300-30-0.05

0Shear Strain0.05

Site A
GL-8.5m0-30050
100σ'm（kPa）
σ'm：Mean Effective Stress(a) Site A
50

Site B
GL-10.5m
Shear Stress(kN/m2)

Shear Stress(kN/m2)

500-50-0.050
Shear Strain0.05Site B
GL-10.5m

0-50060120
σ'm（kPa）
σ'm：Mean Effective Stress(b) Site BFig. 9 Stress-strain relation and effective stress pass
Vertical distributions of maximum soil responses
Figure 10 shows vertical distributions of maximum responses of soil. The soil profile and SPT-Nvalues are also presented. The major difference between site A and site B can be seen in the maximum
shear strains at the liquefied layers.
The maximum horizontal displacement at the ground surface of site A is about 16 cm and that atsite B is about 13 cm. The difference seems relatively small in spite of the occurrence of liquefaction.
The reason for this is that the maximum displacement occurred just before the liquefaction triggeringand moreover that the deformation of the underlying soft silt layers is dominant.

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01010202030

Depth (m)Depth (m)04040

50506030060 0Site A N-Value

100 200 0Acc.
(cm/s2)

10Disp.
(cm)

20 02

ShearStrain(%)

4 00.5601060 0Site B N-ValueP.W.P.R.

(a) Site A

100 200 0Acc.
(cm/s2)1020 0Disp.
(cm)

2ShearStrain(%)

4 00.5

1P.W.P.R.

(b)Site B

Fig. 10 Distributions of maximum responses of soil
Factors affecting the liquefaction triggering
The most influential factor that makes the difference of the liquefaction occurrence in thesesimulations is the difference of the liquefaction strength of the constitutive model at large number ofcycles (Figure 6). The simulation result implies that there is a possibility that the actual difference ofthe liquefaction strength could affect the actual liquefaction extent. However, the bases of determining
the liquefaction strength for both sites are not even (i.e. The basis for site A is the combination ofSPT-N value and the fines content Fc, and the basis for site B is the laboratory testing.). Therefore, wecannot conclude that the difference of the liquefaction strength is the only factor. Further experimental
research on the actual liquefaction strength of the liquefiable layers is necessary.
The other possible factors that could affect the evaluation of liquefaction extent are the borderline
between the reclaimed layer and the underlying natural deposit, the site effect due to the soil structure
below the liquefiable layers, the evaluation of underground water level, and the aging effect on theliquefaction strength. Further research on these factors is also necessary.
Factors affecting the extent of liquefaction damage
As shown in Figure 8(a), the relatively large displacement lasted for long duration after theliquefaction triggering. This means that many times of cyclic deformation occurred in the liquefiedlayer. This post-liquefaction cyclic deformation could be a factor that caused the heavy liquefaction
damage.
Another factor that is not considered in this research is the effect of the aftershock that occurred
about 30 minutes after the main shock. The research on the liquefaction during the aftershock is also
necessary.

CONCLUSIONSThe effective stress analyses of the liquefiable reclaimed ground at two locations along Tokyo Bay809

coast were conducted. One location liquefied and another did not liquefy during the Great East Japan
earthquake. The seismic input motion is relatively small due to the long distance from the epicenter,but has long duration due to the large magnitude. It was found that a small difference of liquefaction
strength could cause a large difference of liquefaction extent. Especially the relatively low liquefaction
strength at large cyclic numbers is important to evaluate the liquefaction extent for the relatively small
but long seismic input motion.

ACKNOWLEDGMENTS
The input acceleration used in this research is a seismic record obtained by Port and Airport ResearchInstitute. The maximum acceleration used in the simplified liquefaction assessment is determinedconsidering the K-net data obtained by National Research Institute for Earth Science and DisasterPrevention. Authors really appreciate both institutes' providing the data.

REFERENCES
Architectural Institute of Japan (2001). “Recommendations for design of building foundations.” (inJapanese)
Architectural Institute of Japan (2006). “Seismic Response Analysis and Design of Buildings
Considering Dynamic Soil-Structure Interaction.” (in Japanese)
Cubrinovski, M. and Ishihara, K. (1998a) “Modelling of sand behavior based on state concept.” Soilsand Foundations, Vol.38, No.3, 115-127
Cubrinovski, M. and Ishihara, K. (1998b), “State concept and modified elastoplasticity for sandmodeling”, Soils and Foundations, Vol.38, No.4, 213-225

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