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

AGING EFFECT ON SAND LIQUEFACTIONOBSERVED DURING THE 2011 EARTHQUAKE AND
BASIC LABORATORY STUDIES
Takaji KOKUSHO1, Yohta NAGAO2, Fumiki ITO2 and Takahisa FUKUYAMA3
1

Professor, Department of Civil & Environment Engineering, Chuo University,
Tokyo, Japan, Kokusho@civil.chuo-u.ac.jp
2
Ex-graduate student, ditto.
3
Graduate student, ditto.

ABSTRACT: During the 2011 Tohoku Pacific Ocean earthquake (M9.0), liquefaction
occurred extensively in reclaimed land in the Kanto plain more than 200 km far from theearthquake fault. The liquefied sand generally contained a lot of non-plastic fines withfines content more than 50% in some places. Almost all sand deposits along the Tokyobay area reclaimed in 1960’s or later liquefied, while in a good contrast, those older thanthat did not, though both had almost identical SPT blow counts. In order to study the
aging effect on liquefaction strength of sands containing fines, a series of basic laboratory tests combining innovative miniature cone penetration and subsequent cyclic undrained loading were carried out in a modified triaxial apparatus on sand specimens containing fines. A unique curve relating cone resistance qt and liquefaction strength RL
was obtained for reconstituted specimens, despite the differences in fines content Fc,
quite contradictory to the current liquefaction potential evaluation practice. Then asmall amount of cement was added to fines in the sand specimens to simulate a geological aging effect in a short time. It was found that the liquefaction strength RL increases
more than the penetration resistance qt, resulting in higher liquefaction strength under thesame cone resistance with increasing Fc. Thus it has been clarified that not the fines
content itself but the aging effect by cementation, which becomes more pronounced insands with higher fines content, can facilitate reasonable basis why liquefaction strength
corresponding to the same penetration resistance is raised with increasing fines content.
In addition, intact samples recovered from in situ Pleistocene and Holocene deposits withknown ages have been tested and confirmed the trends similar to the above results.
Key Words: liquefaction, aging effect, fines content, cone resistance, cementation

INTRODUCTION
During the recent Tohoku Pacific Ocean earthquake (M9.0), liquefaction extensively took place in the
Kanto plain, more than 200 km far from the earthquake fault. Almost all sand deposits along theTokyo bay area reclaimed in 1960’s or later liquefied. In a good contrast, those older than that did
not, though both had almost identical SPT blow counts. The liquefied sand generally contained a lotof non-plastic fines, with fines content Fc more than 50% in many places. In addition to this case,recent case studies reveal that aging effect seems to play an important role in seismic liquefaction of759

sand deposits. Liquefaction mostly occurred in backfills and reclaimed ground of young ages. Also
pointed out is that cases are increasing in which sands containing considerable amount of
low-plasticity fines liquefied such as in Adapazari, Turkey during 1999 Kocaeli earthquake, in
Christchurch during 2010 Darfield earthquake in New Zealand and also in Tokyo Bay area during therecent M9.0 earthquake.
In engineering practice, liquefaction potential is evaluated using penetration resistance in standard
penetration tests (SPT) or cone penetration tests (CPT). If sands contain a measurable amount offines, liquefaction strength is normally raised in accordance to fines content Fc in most liquefaction
evaluation methods. This Fc-dependent modification of liquefaction strength may be originated fromliquefaction case studies (Tokimatsu and Yoshimi 1983, Seed and De Alba 1984), in which empiricalboundary curves, developed in situ, discriminating data points according to liquefaction/non-liquefaction on a chart where seismically induced shear stress was plotted versus SPT
N1-values in many places, were found being strongly dependent on fines content. More directly, Suzuki et al. (1995) carried out CPT tests and soil sampling by in situ freezing technique in the same
sand deposits. The study showed that the higher the fines content the greater the liquefaction
strength for the same qt-value.
In contrast to their finding, however, quite a few laboratory tests using reconstituted specimens,
having the same relative density Dr (e. g. Kokusho 2007) or the same void ratio (Papadopoulou andTika 2008), have shown that RL clearly decreases with increasing fines content of low plasticity finesfrom Fc=0% to 30%. Thus, a lack of understanding seems to remain in the current practice for liquefaction potential evaluation in the field in relation with laboratory test results for sands containing
fines.
The present authors have been carrying out a systematic experimental study in which miniature
cone penetrations and subsequent cyclic loading tests were conducted on the same triaxial test specimens (Kokusho et al. 2005). An innovative simple mechanism introduced in a normal cyclic triaxial
apparatus by Kokusho et al. (2003) was used enabling a miniature cone to penetrate into the sand specimen at a constant speed. The results from the two sequential tests were compared to develop direct
qt - RL correlations for sands containing various amounts of fines.
In the first part of the present paper the aging effect by cementation is investigated in a series oflaboratory tests using reconstituted specimens containing fines. For the aging effect, a small quantityof cement was added to reconstituted specimens to simulate cementation or chemical bonding for ageological time span in a short time. Penetration resistance qt and liquefaction strength RL were
measured in the same specimens to investigate the aging effect on the qt - RL correlations consideringfines content as a key parameter.
In the latter part of the paper, intact specimens sampled from Pleistocene and Holocene deposits
were tested in the same test apparatus to know the direct qt - RL relationship of natural soils. Then,the same soils, disturbed and then reconstituted to the original density, were tested to compare the results with the intact soils from the viewpoint of aging effect.
TEST APPARUTUS, SOIL MATERIAL & TEST PROCEDURES
In the triaxial apparatus used in this research, the specimen size was 100 mm in diameter and 200 mm
in height. In the liquefaction tests, the soil specimen was loaded cyclically by a pneumatic actuator
as a stress-controlled test. In order to carry out a cone penetration test in the same specimen prior to
the liquefaction tests, a pedestal below the soil specimen was modified as shown in Fig.1, so that aminiature cone can penetrate into the specimen from the bottom. For that goal, the pedestal consistsof two parts, a circular base to which the cone rod is fixed and a movable metal cap. Through thecenter of the cap, the cone rod penetrates in the upward direction into the overlying specimen. The
annulus between the two parts is sealed by O-rings, enabling the cap to slide up and down (Kokusho etal. 2003). During the test, the pedestal cap is initially set up at the highest level by filling water in thereservoir, and the specimen is constructed on it. By opening a valve at the start of the cone penetration, the water in the reservoir is squeezed by the cell pressure, resulting in the settlement of a total
body of the specimen at the top of the pedestal. Due to the settlement, the cone penetrates into thespecimen by 25 mm (from initial length 45 mm to final length 70 mm).

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6.0

Miniature cone

6.0
25.0

(Tip angle:60°)

Cone & rod fixed to thepedestal
Movable cap

Strain gauge

Porous metal

Cone rod
Back-pressure
tube

112.0

Water release forcone penetration
Waterreservoir

O-RingWater supply for
initial setup

Gauge signal

Unit (mm)Water releasefor cone
penetration

Water supply
to insidereservoir

Fig. 1 Cross section (right) and Photograph (left) of the modified pedestal
in the lower part of triaxial apparatus
The penetration speed is about 2mm per second, much slower than prototype CPT and is almost
constant irrespective of the difference in relative density. The miniature cone is 6 mm diameter and
60 degrees tip angle, about 1/6 smaller in dimension than the prototype cone used in the field. The
strain gauges to measure the penetration resistance are glued at the inner wall of the rod tube, 25 mm
lower than the foot of the cone.
Beach sand (Futtsu sand) consisting of sub-round particles of hard quality was used for reconstituted specimens. Fines mixed with the sand was silty and clayey soils with low plasticity index of
Ip=6 sieved from decomposed granite in reclaimed ground of the Kobe city, Japan. For the test series
for cementation, a prescribed quantity of Portland cement was completely mixed with the Masa finesoil to make it with different degree of chemical activity. The cement content Cc, the weight ratio of
cement to soil (including fines), varied from 0 to 1.0%, and the fines content Fc including the cementchanged from 0 to 30%. This means that the ratio Cc/Fc, a parameter representing chemical activityof fines, varied from 0 to 30%. Then the sand specimen with given Fc was prepared by the wet
tamping method to make a given relative density Dr, which was changed in 3 steps, about Dr=30, 50
and 70%. The specimen was then completely saturated with de-aired water, and consolidated under
the isotropic effective stress of 98 kPa with the back-pressure of 196 kPa. If cement is added to fines,
the consolidation time was controlled exactly 24 hours after wetting, while for tests without cement it
was about 2 hours.
Then, the specimen was fully saturated by using de-aired water in a double negative pressure
method so that the B-value larger than 0.95 was measured, and isotropically consolidated with the effective stress of 98 kPa with the back-pressure of 196 kPa. In the test sequence, the penetration test
was first carried out under undrained condition after consolidating the specimen. Then, after releasing pore pressure and reconsolidating it under the same confining pressure again, although the volume
change by this procedure was almost negligible, the liquefaction test was carried out on the same specimen. The sinusoidal cyclic axial load applied with the frequency of 0.1 Hz was measured with a loadcell in the pressure chamber. The cell pressure and the pore-water pressure were measured withelectric piezometers and the axial deformation is measured with LVDT of 50 mm maximum capacity.
It may well be suspected that, in such a test sequence, the liquefaction strength is possibly influenced
by the preceding cone test and subsequent reconsolidation. However, it was already confirmed in previous research (Kokusho et al. 2005) that the cyclic stress ratio for liquefaction was almost unaffectedby the cone test and reconsolidation.

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RESULTS ON RECONSTITUTED SPECIMENS WITHOUT & WITH CEMENT

Cone resistance (MPa)In the test, relative density Dr, fines content Fc and cement content Cc of the specimen were parametrically changed to investigate their effects on penetration resistance and undrained cyclic strength.
Figs. 2(a)-(e) show cone resistance qt and associated excess pore-pressure u plotted versus the penetration length L in the tests for Dr≈50%, Fc=0, 5, 10, 20, 30% and Cc=0, 0.5, 1.0%. It is clearlyobserved that qt for soils without cement (Cc =0) decreases with increasing fines up to Fc =20%. For
individual Fc–values, qt tends to increase more or less with Cc increasing from 0 to 1%. The increaseis particularly large for Fc =20% and Cc=1%. The excess pore pressure u building up almost linearly with the penetration length L tends to decrease with increasing Cc. In Figs. 3(a), (b), similar
Futtsu sandWet tampings c’=98kPa

Cc =0%
Cc =0.5%
Cc =1%

Cone resistance (MPa)
Excess PP. (MPa)

0.03

4

2

2

0

1

2

3

0
0

0.03

0.03

0.02

0.02

0.01

0.01

0.00

(c) Fc=10%

8

6

4

0

(b) Fc=5%

8

6

Excess PP. (MPa)Dr ≒50%(a) Fc =0%

8

0

4

(d) Fc=20%

6

4

2

2

0

0

2

3

0
0

1

2

3

0

0 .03

0 .0 3

0.02

0 .02

0 .0 2

0.01

0 .01

0 .0 10 .00

0 .0 00.000(e) Fc=30%

8

6

4

1

3

0.00

2
0

2

1
2
3
1
2
3 0
Penetration length (cm)Penetration length L (cm)

8

6

1

1
2
3 0
1
2
3
Penetration length L (cm) Penetration length L (cm)

0

1

2

3

1
2
3
Penetration length L (cm)(a) Dr≒30%

8
6
4
2
0

0

1

2

3

Cone resistance (MPa)Cone resistance (MPa)Fig. 2 Cone resistance or excess pore-pressure versus penetration length L
for reconstituted specimens of Dr ≈ 50% with different fines content.

Fc=0%
Fc=5%
Fc=20%

0.06
0.04
0.02
0.00

0

1

2

Penetration length L (cm)3

Excess PP. (MPa)

Excess PP. (MPa)0.08(b) Dr≒70%

8
6
4
2
0

0

1

0.08

2

3

Fc =0%
Fc =5%
Fc =10%Fc =20%

0.06
0.04
0.02
0.00

0

1

2

Penetration length L (cm)3

Fig. 3 Cone resistance or excess pore-pressure versus penetration length L
for reconstituted specimens of Dr≈ 30% & 70%with different fines content without cement.

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penetration test results are shown for sands of Dr≈30% and 70% with varying Fc but no cement. It isobserved again that the increase in Fc tends to decrease cone resistance qt..
Figs. 4 (a)-(e) show relationships between the cyclic stress ratios R ( s d 2s c¢ : s d =cyclic stressamplitude, s c¢ = effective isotropic confining stress) versus the number of loading cycles Nc for the
double amplitude axial strain ɛDA=5% obtained by undrained cyclic loading tests on sand specimens
having Dr≈50%, Fc=0, 5, 10, 20, 30%, and Cc=0, 0.5, 1.0%. Obviously, the increase in fines content
tends to reduce stress ratio R in specimens without cement as already demonstrated by previous researches (e.g. Kokusho 2007). Also indicated in the figure is that the R-value increases with increas-

Cyclic stress ratio (ε DA=5%)

Futtsu sandWet tampings c’=98kPa

0.3

C c =1%

0.2

C c =0.5%
C c=0%

0.1(b) Fc =5%
0.0
0.1

1
10
100
1000
Number of loading cycles Nc

0.4
0.3

C c =1%

0.2
Cc =0.5%
0.1(d) F c =20%
0.0
0.1

C c=0%

1
10
100
1000
Number of loading cycles Nc

Cyclic stress ratio (ε DA=5%)

0.4

Cyclic stress ratio (ε DA =5%)

Cyclic stress ratio (ε DA =5%)

Cyclic stress ratio (ε DA=5%)

Dr≒50%

0.4
0.3

C c=1%

0.2

Cc =0.5%
Cc =0%

0.1(a) Fc =0%

0.0
0.1

1
10
100
1000
Number of loading cycles Nc

0.4
0.3
C c =1%
0.2
C c =0.5%
C c =0%0.1(c) F c=10%
0.0
0.1

1
10
100
1000
Number of loading cycles Nc

0.4
0.3
C c=1%
0.2
C c =0.5%
0.1(e) F c =30%

0.0
0.1

C c =0%

1
10
100
1000
Number of loading cycles Nc

0.4
0.3

(a) Dr≒30%, Cc=0

Fc =0%
Fc =5%
Fc =20%

0.2
0.1
0.0
0.1

1
10
100
1000
Number of loading cycles Nc

Cyclic stress ratio (εDA=5%)

Cyclic stress ratio (εDA=5%)

Fig. 4 Stress ratios R versus number of loading cycles Nc for reconstituted specimens of Dr≈50%
with different fines content.
0.4(b) Dr≒70%, Cc=0

0.3
0.2

Fc =0%
Fc =5%
Fc =10%Fc =20%

0.1
0.0
0.1

1
10
100
1000
Number of loading cycles Nc

Fig. 5 Stress ratios R versus number of loading cycles Nc for reconstituted specimens
of Dr≈30% & 70% with different fines content without cement.

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Liquefaction strength RL ( DA=5%,Nc=20)

ing cement content for all the fines content Fc and the increment is larger for Cc=1% and Fc =10 -30%.
In Fig. 5(a), (b), the similar liquefaction strength results are shown for specimens with Dr≈30%, 70%
with varying Fc but no cement. Again, the increase in Fc obviously decrease the stress ratio R for
dense sand of Dr≈70% in particular.
In Fig. 6, test results for different values of Dr, Fc and Cc are shown on the RL ~ qt diagram withdifferent symbols. The liquefaction strength RL in the vertical axis is defined as the stress ratios d 2s c¢ for ɛDA=5% and Nc=20. The penetration resistance qt in the horizontal axis is determined as
the maximum value of the cone resistance during penetration from the qt ~ L curves shown in Figs. 2
and 3. The open symbols in Fig. 6 along the thick dashed line which correspond to the specimens
without cement are located along the thick dashed line in the chart despite wide differences in Dr(30~70%) and Fc (0~30%) as already pointed out in the previous research (Kokusho et al. 2005, 2009),
indicating that the liquefaction strength RL is uniquely correlated to qt irrespective of Fc. This finding
is contradictory with the current liquefaction potential evaluation practice, where RL is raised accordDr=50%,Fc=0%, Cc=0%
Dr=50%,Fc=0.5%, Cc=0.5%
Dr=50%,Fc=1%, Cc=1%
Dr=50%,Fc=5%, Cc=0%
Dr=50%,Fc=5%, Cc=0.5%
Dr=50%,Fc=5%, Cc=1%
Dr=50%,Fc=10%,C c=0%
Dr=50%,Fc=10%,C c=0.5%
Dr=50%,Fc=10%,C c=1%
Dr=50%,Fc=20%,C c=0%
Dr=50%,Fc=20%,C c=0.5%
Dr=50%,Fc=20%,C c=1%
Dr=50%,Fc=30%,C c=0%
Dr=50%,Fc=30%,C c=0.5%
Dr=50%,Fc=30%,C c=1%
Dr=30%,Fc=0%, Cc=0%
Dr=30%,Fc=5%, Cc=0%
Dr=30%,Fc=20%,C c=0%
Dr=70%,Fc=0%, Cc=0%
Dr=70%,Fc=5%, Cc=0%
Dr=70%,Fc=10%,C c=0%
Dr=70%,Fc=20%,C c=0%

0.4

0.3

0.2

0.1

0.0

0

1

2

3

4

5

6

7

8

Penetration resistance qt (MPa)Liquefaction strength RL ( DA=5%, Nc=20)

Fig. 6 Liquefaction strength RL versus penetration resistance qt diagramfor different values of Dr, Fc and Cc.
1.2
Suzuki et al. 1995
Fc<1%1%< Fc <10%10%< Fc

1.0
0.8

Other symbols are
the same as in Fig.6.

0.6

Fig. 6

0.4
0.2

Present test (Cc=0)

0.0

0

5

10

15

20

25

Penetration resistance q t (MPa)Fig. 7 Liquefaction strength RL versus penetration resistance qt compared withL
field investigations combining prototype
CPT and triaxial tests ont intact samples.

764

ing to Fc.
The half-close and close symbols in Fig. 6 are from the accelerated tests on specimens containing
cement. Among them, upward triangles, for instance, represent the case Fc=5%, and they move up
from the open (Cc =0) to the half-close (Cc =0.5%) further to the full-close symbols (Cc =1.0%) as Cc /Fc changes from 0 to 20% for the same value of Fc =5% as indicated by thin arrows in the diagram.
In the similar manner, other symbols move up with increasing Cc or Cc / Fc for the same fines content
of Fc =10%, 20% and 30%. Samples with higher value of Cc / Fc may be considered as of longer
geological age because higher chemical activity is exerted in the same soil in the accelerated test.
This indicates that the cementation effect tends to push up the data points on the RL ~ qt diagram fromthe unique line of no cement and gives higher liquefaction strength under the same cone resistance.
In Fig. 7, the same data points as in Fig. 6 are plotted again together with star symbols
representing in situ soil data by Suzuki et al. (1995). In their research, prototype cone tests in situ
and laboratory undrained cyclic triaxial tests on intact samples recovered from the same soil deposits
by in situ freezing technique were combined. It demonstrates a clear difference in the RL ~ qt relationships due to different fines contents of Fc <1.0%, Fc =1.0-10% and Fc >10%. Also noted is thatthe two research results are in a good coincidence not only qualitatively but also quantitatively, particularly in the case without cement, despite a large difference in the cone size and CPT test procedures.
Based on the data shown in Fig. 6, the ratio of increase in RL or qt with respect to those without
cement is shown versus the Cc /Fc -value with the fines content Fc as a parameter in Fig. 8. With increasing chemical activity Cc/Fc , the RL-value increases more than the qt-value for Fc £ 10%, but it isreverse for Fc ³ 20%. Also noted in Fig. 8 is that not only the Cc /Fc -value but also the fines content
Fc increasing up to Fc=20% tends to considerably increase RL and qt even under the same cement con8
RL/ RL Cc=0%

qt/qt, Cc=0%, RL/R L, Cc=0%

7

qt/ qt Cc=0%

6
Cc = 1 %

5
4
3
2
1
0

0

5

10

15

20

25

Relative cement content in fines C c / Fc (%)

Fig. 8q /qtt, Cc=0%or R /RL

versus Cc/Fc

L, Cc=0%

Stress ratio RL (DA=5%, Nc=20)

0.4
Fc = 20%
Cc / Fc = 5%

Fc = 10%
Cc / Fc = 10%

0.3

0.2

Fc = 10%
Cc / Fc = 5%

0.1

0.0

Fc = 5%
Cc / Fc = 10%

0

2

4

6

8

Cone resistance qt (MPa)Fig. 9 Close-up of Fig. 6 showing the effect of fines content Fc for the same Cc/Fc.

765

tent of Cc =1.0% as demonstrated by the encircled plots but the trend seems to change at Fc=30%.
Thus, there seems to be a kind of transition between Fc=20% and 30%, where the increasing trend in
RL or qt with increasing Cc /Fc -value changes. This may possibly have something to do with thechange in soil fabric from grain-supporting to matrix-supporting structure.
In Fig. 9, where the same data as in Fig. 6 are plotted again, it is recognized that the plot for Cc /Fc–value, 5% or 10% shifts upward as Fc increases from the unique line of no cement as indicated by the
thick arrows in the graph. This indicates that, for the same Cc /Fc –value (simulating the same geological age), higher Fc-value results in higher liquefaction strength for the same cone resistance. This
trend is compatible with the liquefaction potential evaluation practice currently employed. Thus, thepresent research results by the accelerated test clearly indicate that not the fines content itself but thecementation effect is responsible for the higher liquefaction strength for larger Fc under the same cone
resistance.
TEST RESULTS ON IN SITU INTACT SPECIMENS
In order to know the direct RL ~ qt relationship of natural soils and compare them with the accelerated
test results on reconstituted soils using small amount of cement mentioned above, intact soils havebeen sampled from in situ soil deposits. They have been tested in the same way to measure mini-cone
penetration resistance and undrained cyclic strength for the same specimens. Pleistocene sands andHolocene sands have been recovered from two sites in the Kanto area near Tokyo by block sampling
using PVC tubes as shown in Fig.10. The size of the PVC tube was 120 mm in inner diameter and
200 mm in height, and a circular metal cutting edge was attached to the tube to penetrate it slowly into
sampled soil.
Pleistocene soil was taken from two sand deposits A and B inter-bedded in a river terrace near
Narita-city in Chiba Prefecture. Their ages were estimated about 100 ×103 and 150×103 years old,
respectively (Mitani 2006). The overburden depth was about 5 m and 11 m for the two soils, A and B,
respectively. The relative density and fines content of A are Dr=101-107% and Fc=6.1-8.5%, andthose of layer B are Dr =75-81% and Fc =12-19%, respectively. Samples taken out in PVC tubes
were frozen in the laboratory and then trimmed into the specimen of 100 mm in diameter and 200 mm
in height, because it was difficult to handle them without freezing.
Holocene soil with Dr =35-81% and Fc=13-25% was taken from a river terrace sand layer in Tateyama-city in Chiba Prefecture by using the same PVC tubes. Its age was estimated 2-4×103 years
old (Shishikura 2005). The overburden depth for the soil was about 5m. For this soil, it was possible to trim the sample into the specimen size without freezing.

Fig. 10 Photographs of block sampling using a PVC tube with metal edge at the tip(Left: Pleistocene sand, Right: Holocene sand)

766

8

Cone resistance qt (MPa)

(a)
6

4

2

0

Excess pore-pressure Du (kPa)

0.0

0.5

1.0

1.5

2.0

2.5

3.0

Pleistocene (intact: freeze+thaw)
A: Fc=6.1-8.5%, Dr=102-108%
B: Fc=12.1-18.7%, Dr=75-81%%
Pleistocene (reconstituted)
A: Fc=7.8%, Dr=97-103%
B: Fc=15.3%, Dr=74-82%
Holocene (intact) Fc=13-25%
Dr=81%
Dr=35%
Dr=56%
Dr=78%
Dr=40%
Dr=55%

40
35
30
25
20

(b)

15
10
5
0
0.0

0.5

1.0

1.5

2.0

2.5

3.0

Penetrion length L (cm)Cyclic stress ratio R (eDA=5%)

Fig. 11 Cone resistance (a) or excess pore- pressure (b) versus penetration length L
for intact and reconstituted Pleistocene/Holocene sands.

Pleistocene (All data MP Modified)Intact A: Fc=6.1-8.5%, Dr=102-108%
Intact B: Fc=12-19%, Dr=75-81%%
Recon. A: Fc=7.8%, Dr=97-103%
Recon. B: Fc=15.%, Dr=74-82%

0.4

(a)
0.3

Intact B RL=0.207
Intact A RL=0.197

0.2

Recon. B RL=0.144

Recon. A RL=0.142

0.1
1Cyclic stress ratio R (eDA=5%)

0.3

10

(b) Dr=78-81%, Fc=25%

0.2

20

100

Dr=35-40%, Fc=19%

Intact RL=0.192
Recon. RL=0.151

Dr=55-56%,
Fc=13%

Holocene (All data MP modified)Intact Fc=13-25%, Dr=35-81%
Recon. Fc=13-25%, Dr=39-78%
0.1
1

10

Number of loading cycles Nc

100

Fig. 12 Stress ratios R for e DA = 5% versus number of loading cycles Nc
for intact specimens from Pleistocene sands.

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A hole for the mini-cone was drilled in advance at the center of the specimen bottom with a drill
bit, 6 mm in diameter and 43 mm in depth (2mm shorter than the cone length). It was then set on thepedestal of the modified triaxial apparatus. The specimen was fully saturated with de-aired water tosecure the B-value larger than 95%, consolidated by isotropic pressure of p’0=98 kPa for all the intact
samples. Then, the mini-cone penetration test was conducted in undrained condition. After that,the specimen was reconsolidated by p’0=98 kPa and undrained cyclic test was carried out in the samemanner as in the reconstituted specimens mentioned before.
Fig. 11 shows cone resistance qt and associated excess pore-pressure u plotted versus the penetration length for intact Pleistocene soils A and B with thick curves. The corresponding data arealso shown with dashed curves for reconstituted specimens, which were once disturbed and compacted
in a mold by moist-tamping method to reproduce the same in situ density. Despite some data dispersions, the cone resistance qt for intact soils is generally larger than that for reconstituted soils. The
mini-cone data for Holocene soils are superposed in Fig. 11 with thin curves. The difference in qt
between intact and reconstituted specimens is again obvious despite wide variation in Dr among thespecimens.
In Fig. 12, the cyclic stress ratios R= s d 2s c¢ for axial strain e DA = 5% are plotted versus thenumber of load cycles obtained from cyclic loading tests conducted for the same intact or reconstituted
specimens of Pleistocene and Holocene soils after the mini-cone penetration tests. For intact specimens, the R-values have been modified considering the effect of rubber membrane penetration becauseof their rugged side face. Even for the reconstituted specimens, the MP correction has been foundnecessary and implemented, in contrast to Futtsu beach sand, previously mentioned, in which the MP
effect was negligible. For the Pleistocene soils shown in (a), R-values of intact specimens are evidently larger than those of reconstituted soils in spite of the data dispersions. For the Holocene intact
soils in (b), the data points on the R – Nc chart seem to be consistently plotted not only for intact but
also for reconstituted specimens, despite the big difference in Dr as indicated in the chart. The
R-values of intact specimens are again evidently larger than those reconstituted. From Fig 12, theliquefaction strength (cyclic resistance ratio) RL defined as R for e DA = 5% and Nc=20 was read off as indedicated in the chart for intact or reconstituted specimens of each soil.
In Fig. 13, the liquefaction strength RL and penetration resistance qt for Pleistocene and Holocene
soils are directly compared on the RL ~ qt diagram using different symbols. The liquefaction strength
RL in the vertical axis is defined as the stress ratio R for ɛDA=5% and Nc=20 as indicated in Fig. 12.
The penetration resistance qt is determined as the maximum value of the cone resistance during penetration from the qt ~ L curves shown in Fig.11. The qt–value in the horizontal axis of Fig. 13 is theaverage for 3 to 4 penetration tests on the same soil.
Pleistocene(Large:average, Small: individual)
Intact A: Fc=6.1-8.5%, Dr=102-108%
Intact B: Fc=12.1-18.7%, Dr=75-81%
Recon. A: Fc=7.8%, Dr=97-103%
Recon. B: Fc=15.3%, Dr=74-82%
Holocene(Large:average, Small: individual)
Intact A: Fc=6.1-8.5%, Dr=102-108%
Recon. A: Fc=7.8%, Dr=97-103%
Reconstituted Futtu sand
Fc=0-30% Dr=30-70%)

Stress ratio RL (eDA=5%, Nc=20)

0.4

0.3

0.2

0.1

0.0
0

2

4

6

8

10

Cone resistance qt (MPa)Fig. 13 Stress ratios RL versus cone resistance qt of intact Pleistocene and Holocene soils
compared with reconstituted specimens.

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The cross symbols in Fig. 13 indicate the RL ~ qt plots obtained for Futtsu beach sand with varying Fc , which are exactly the same data points without cement in Fig. 6. As already explained, they
are located along the thick dashed line irrespective of differences in Dr and Fc. Obviously, the plotsof intact soils (the solid symbols) are located higher than the thick dashed line. The reconstituted
specimens of in situ soils are not completely coincident with the thick dashed line but slightly higher
than that. However, the plots for intact soils (the solid circle and triangle) are found still higher thanthose of the reconstituted soils if the lines parallel with the thick dashed line passing through them arecompared. The difference in the parallel lines between intact and reconstituted is larger for Pleistocene than for Holocene, seemingly reflecting the difference in ages. More test data on in situ soils
are needed to know exactly the aging effect on the plots considering the effect of fines content of Fc.
CONCLUSIONS
During the 2011 Tohoku Pacific Ocean earthquake (M9.0), liquefaction occurred extensively in reclaimed land in Kanto area more than 200 km far from the earthquake fault. The liquefied sand generally contained a lot of non-plastic fines with fines content more than 50% in some places. Almost
all sand deposits along the Tokyo bay area reclaimed in 1960’s or later liquefied, while in a good contrast, those older than that did not, though both had almost identical SPT blow counts. The first partof the paper contributes to basically understand the aging mechanism for liquefaction by conducting aseries of experimental study by miniature cone penetration tests and subsequent cyclic loading tests inthe same triaxial test specimen with fines content Fc as a key parameter. Accelerated tests on the
cementation effect using Futtsu beach sand without or with a small quantity of cement yielded the following major findings;
・ For reconstituted sands without cement, the liquefaction strength RL is uniquely related to the cone
penetration resistance qt, forming a single RL ~ qt line, irrespective of fines content Fc, quite contradictory to the current liquefaction potential evaluation practice where RL is modified according
to Fc.
・ This laboratory test result coincides with in situ RL ~ qt relation by Suzuki et al.(1995) quantitatively despite clear difference in the test procedures and cone size.
・ Specimens with higher value of Cc/Fc (simulating longer geological age) results in higher liquefaction strength under the same cone resistance, indicating that the cementation effect tends toraise the RL ~ qt line from that for soils without cement (without aging effect).
・ For the same Cc/Fc-value (simulating the same geological age), higher fines content results inhigher liquefaction strength RL under the same cone resistance qt, which is consistent with thetrend found in the field investigations.
In order to examine that the above test results are consistent with natural deposits of long geological ages, intact specimens sampled from Pleistocene deposits (100-150×103 old) and Holocene deposits (2-4×103 old) were tested in the same way to know the direct RL - qt relationship of natural soils
and compared with reconstituted soils, yielding the following;・ Differences are clear in both penetration resistance qt and liquefaction strength RL between intact
and reconstituted specimens of Pleistocene or Holocene deposits.
・ Direct relationship between RL and qt is found compatible with that of the accelerated tests using
cement, so that the RL - qt line of intact specimens is located higher than that of reconstituted specimen. The difference between the lines seems to be larger with geological ages.
Consequently, the series of tests on reconstituted and intact natural sands revealed that the reason
why higher fines content leads to higher liquefaction strength does not depend on fines content itself
but cementation effect, which tends to be pronounced as fines increase. This further indicates thatthe current practice on liquefaction resistance modification by fines content may lead to dangerous
results if it is applied to very young deposits. In this vein, the ages of reclaimed lands, which generally contained a plenty of non-plastic fines, may have made differences during the Tohoku Pacific
Ocean earthquake in liquefaction susceptibility of reclaimed lands despite their similar soil conditions.
Needless to say, more tests on in situ soils are needed in order to quantitatively propose an empirical formula for revising current liquefaction potential evaluation methods considering the aging
effect in conjunction with the effect of fines content.

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ACKNOWLEDGMENTS
Geologists and experts in Quaternary geology in Japan, Y. Mitani, S. Ishiwata and Y. Momikura, whokindly provided the authors with publications on the local geology and guided us to outcrops of known
ages for block sampling are gratefully acknowledged.
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