Proceedings of the International Symposium on Engineering Lessons Learned fromthe 2011 Great East Japan Earthquake, March 1-4, 2012, Tokyo, JapanBEHAVIOR OF LIQUEFIED SOIL NEAR BOUNDARY
OF BACKFILLED BASIN DUE TO MAIN AND
FOLLOWING MUXIMUM AFTERSHOCK
Atsuo ONOUE1, Fei CAI2, Miyoko NAKAJIMA3, Masayoshi NISHIKAWA4,
Takashi TORIGOE5, and Kumiko YONEDA6
1

Technical Advisor, Engineering Department, Koa Corporation,
Tokyo, Japan, atsuo.onoue@koa-kaihatsu.co.jp
2
Research Associate, Department of Civil and Environmental Engineering, Gunma University,
Gunma, Japan, feicai@gunma-u.ac.jp
3
Head, Laboratory, Koa Corporation, Tokyo, Japan, miyoko.nakajima@koa-kaihatsu.co.jp
4
Sub Head, Laboratory, Koa Corporation, Tokyo, Japan, masayoshi.nishikawa@koa-kaihatsu.co.jp
5Senior Engineer, Laboratory, Koa Corporation, Tokyo, Japan, takashi.torigoe@koa-kaihatsu.co.jp
6
Senior Engineer, Laboratory, Koa Corporation, Tokyo, Japan, kumiko.yoneda@koa-kaihatsu.co.jp

ABSTRACT: Reclaimed lands backfilled by the remainder which collected iron content
in the iron ore sand deposits were liquefied in Asahi City, Chiba Prefecture due to the2011 off the Pacific coast of Tohoku Earthquake. Based on the site investigations and thenumerical analysis, the behaviors of the liquefied soil at the brinks of the backfill basins
were classified into three types, namely heave, cave-in and landslide. The mechanism ofthese behaviors was attributed to the relationship between the predominant direction of
displacement of liquefied soil and the location of the excavation boundary.
Key Words: Great East Japan earthquake, iron ore sand, liquefaction, upheaval,
excavation boundary, interview, damage, numerical analysis

INTRODUCTION
Foundations liquefied at various places in the Kanto district due to the 2011 off the Pacific coast of
Tohoku Earthquake (MLIT and JGS 2011). Most of them are the lands reclaimed after 1965 along thecoast of Tokyo Bay, old river channels and flood plains of the Tone River, developed lands at old
ponds and marshes reclaimed by dredge sand. In addition, severe liquefaction occurred here and thereat reclaimed lands backfilled by discarded sand from iron ore production at the iron ore deposits in
Asahi-city, Chiba prefecture.
Though it is well known that the typical soil behaviors due to liquefaction are the land slide at aslope, the lateral flow near quays, subsidence of horizontal ground, sink of heavy structures andfloating up of light underground structures such as a sewage tank (Onoue et. al. 2011), rise and cave-inof the ground and wave-like undulations were also conspicuous in addition to those in Asahi-city
during the present earthquake. This paper reports investigation results about behaviors of foundation

777

due to liquefaction observed at old iron ore deposits in Asahi-city and new geotechinical findings
obtained through a numerical analysis on the liquefaction.

OUTLINE OF INVESTIGATION
Locations of iron ore sand deposit and liquefied areas
The areas where liquefaction damage was remarkable in Asahi-city are shown by the ellipses in Fig.1.
The iron ore sand deposits located in old Iioka-town are described in the History of Iioka-town(Iioka-town 1981). Although all the locations of these iron ore sand deposits were indicated in Fig. 1
with broken lines, some of them have not been excavated in the past as a mine. Moreover, although
there are many places where a liquefied area does not overlap with the position of the ore deposit on amap, at least all the liquefied lands were reclaimed by iron ore sand according to the reports of theearthquake victims. The areas where iron sand has been excavated are, therefore, more than thoseindicated in Fig. 1 including ellipses indicated in old Asahi-city (left half of Fig. 1).
Hebizono
Iron sand ore
deposit （according toHistory of
Iioka town)
Traces ofliquefaction,such as sandejecta, uplift ofundergroundtank, etc.

Higashi sokusen

Ushirogusa

Sangawa

Ashikawa

Nakayari
Shiinauchi
Ashikawahama

500m
N

Jinguji
Komagome

Fig.1 Liquefied areas and distribution of iron ore sand deposits in Asahi city
Summary of reconnaissance and following investigation
Deformations and cracks of foundation, subsidence and tilting of buildings and telegraph poles, upliftof underground structure, sand ejection, etc. were observed on-site. Interview with victims, land
surveys of deformed foundation, in-situ soil investigation through Swedish Weight Sounding (SWS),
and laboratory tests on the intact samples taken on-site were performed. The time when liquefaction
occurred was inspected through a two dimensional liquefaction analysis based on the laboratory test
results.

778

RESULTS OF INVESTIGATION
Out of many liquefied areas shown in Fig.1, a close view of the Ushirogusa and Hebizono areas wherequite a few houses suffered great damage due to liquefaction are shown in Fig. 2. The Nakasone zone
in the Hebizono area shown in the region surrounded by the solid line was a residential area developedon the land backfilled after iron ore mining. This zone suffered such devastating damage that 40
houses out of totally 48 houses were judged to be totally destroyed. According to explanations given
by both owners of excavated land and unexcavated land, the boundary of the excavated and backfilledarea is the solid lines in Fig. 2.

Ushirogusa

Hebizono

Reclaimed
old pond

2

Nakasone zone
2

1

34

1(b)
1（a）

N

5

6
7
8
3

Legend４

Crack with steps

1(a) ～

Reclaimed
old pond

1～

6

6： Photo number
8：Swedish Weight Sounding

100m：Excavated and backfilled zone

Fig.2

Location of soil investigations, photos and remarkably damaged foundations

Ushirogusa area
Photo 1(a) shows an example of vast sand ejected due to the main shock and Photo 1(b) shows a traceof ejected sand remaining on the wall. The trace indicates that the thickness of the ejected sand was 60
cm here. The grain size distributions of liquefied sand sampled at Ushirogusa and Hebizono are shownin Fig.3. It shows markedly inferior distribution of fine sand having a uniformity coefficient of 2.
Figure 4 shows equivalent SPT N-value converted from the results of SWS conducted at theUshirogusa and Hebizono areas. According to this figure, the depths of water table in this area areabout 1.3 m and the excavation depths of iron sand ore ranges from 3.5 m to 4 m below the groundsurface. The thickness of liquefied sand portion appears to be as thin as 2 to 3 m.

60ｃｍ(a) Spouted sand (25 minutes after(b) Trace of sand spout
the main event, Photo: Ikeda)
Photo 1 Sand ejecta and its trace observed at Ushirogusa area779

Percentage finer （％）

100
Ushiroguza
後草ρs=3.051

80

Hebizono
蛇園（畑）ρs=2.876ρs=2.87660

浅間神社南South ofShrineρs=2.93440ρs=2.934

20
0
0.01

0.1

1
Grain size （mm）

10

Fig.3 Grain size distribution and specific gravity of soil
Ushirogusa area

Hebizono area

Equivalent N value

Equivalent N value

1.27

1.54

Depth （ｍ）

1.39

1.78

Excavation
depth ：3.5～４m

Excavation
depth ：4.5～5.5m

Fig.4 Equivalent N-values based on the result of SWS
Nakasone zone in Hebizono area
Upheaval of land
Photo 2 shows the site to the north of SWS No.2 location where sand spout was observed during thelargest aftershock. Although no damage was seen regarding the ground in the near side of this photo, acrack with a level difference appeared along the line connecting the entrance terrace and the car, andthe ground heaved up at far side of the line. This site is located at the upper left corner in Fig. 6 with
its enlarged map. The results of level survey were shown along the three survey lines, A –A’, B – B’
and C – C’ in Fig. 6. Photo 2 was taken at Point B viewing Point B’. According to the survey results
along B – B’ and C – C sections, the ground rose by 60 cm and by 38 cm, respectively, in the right sideof the crack. The direction of the ridge of upheaval is almost the east - west. The ridge is parallel to theboundary between the excavated and the unexcavated lands, and the distance between them is about
30 m. The down-ward arrows, (↓), noted as “Excavation boundary”in Fig.6 show the estimatedlocations of the excavation boundary. The white arrows show the estimated predominant directions ofliquefied sand motion. For instance, the excavation boundary is located in the direction of A’-B’-C’side for this residential land in Photo 2. Rise of the soil liquefied at the inside of the boundary meansthat liquefied sand at A-B-C side is considered to have moved mainly to the direction of the boundary.
Cave-in means, to the contrary, that the liquefied sand moved mainly in the direction which keeps
away from the boundary.

780

Risen partNo damage

Photo 2 Upheaval of housing lot at Hebizono area
Photo 3 shows a ground deformation near the boundary. The waterway, the retaining wall on theleft and the rice field on the left in far side in the figure were not damaged because they are located in
unexcavated part. To the contrary, the ground heaved up and the waterway was collapsed anddisappeared on near side which is located in the excavated and backfilled part. Photo 4 shows a house
which was greatly bent into a mountain shape since the site heaved up near the middle of the house.

Waterway without damage

Waterway
disappeared
by upheavalof the ground.

Photo 3 Boundary between unliquefied foundation and damaged foundation

Risen part of groundBroken house inreversed V shape

Photo 4 Destroyed house due to ground upheaval at the center of the house781

About 60 cm

The cultivated field shown in Photo 5 is located in the excavated side and the excavation boundary
is located on the left side of this photo. Although this field had been flat and no sand spout wasobserved during the main shock, it heaved up with ejects of sand during the largest aftershock at
approximately 15:15. Photo 5 shows the middle and upper steps having a height difference of 60 cm.
According to E – E’ section in Fig. 6, elevations of the middle step and the upper step were 25 cm
and 85 cm higher than that of Point E on the lower step which has not liquefied because of belonging
to the unexcavated side. Figure 5 shows the equivalent N-value along E – E‘ section. The
unexcavated ground is so stiff at depths deeper than 2 m that the equivalent N-values are larger than
40. To the contrary, the backfilled sand is so loose that the equivalent N-values are less than 10 ingeneral to the depth of 6 m to 6.5 m, though they exceed 15 at some depths.
The mechanism of the ground upheaval all at once at the inside of the excavation boundary is
considered to be as follows: The foundation had not reached near complete liquefaction with sandejection, though the excess pore water pressure increased to considerably large. It liquefied almost
completely and the sand was ejected during the following largest aftershock. When the liquefied soil
moved toward the un-excavated foundation, it heaved up because it was blocked in the hard stratum
and rose. It is imagined that the ground heaved up to the broken line indicated in Fig.5 just after risingand subsided to the solid line with increasing elapsed time. Along the survey line D – D’, themaximum value of upheaval was 80cm here.

Upper step

Middle step
Photo 5 Up-heaved field due to liquefaction of soil
Non-excavated

Dense
sand

Middle bench

Loose
sand

SWS8

Lower bench

Heave
After subsequentsubsidence

SWS7

Depth （ｍ）

0.83m

Lower
bench

Upper
bench

Middlebench

SWS6

Equivalent N value

Reclaimed after excavation

Force of inertia

Upper bench

Seismic motion

Dense sandFigure 5 Schematic picture of upheaval mechanism

782

Excavation
boundaryF’

Excavation
boundaryG

Excavation
boundaryF
G’？
Unexcavated side

Excavation
Aboutboundary
30m

Excavation
boundary

H

Excavation
boundary

Excavated
side

D’

H’

D
I
Excavation
boundary？

E’
Excavation
boundaryE

Unit: vertical axis [ cm ], horizontal axis [ m ]

I’

100m

Excavation
boundary

Scale：Predominant displacement direction of liquefied soil

Fig.6 Upheaval, cave-in and slope failure due to liquefaction at the peripheryof backfilled discarded iron ore sand (Nakasone zone in Hebizono area）
Landslide
Along F – F’ survey line in Fig.6, the slope failure with the main scarps were observed as indicated in
the schematic picture. A tremendous amount of ejected sand was observed in the field around Point F.
Therefore, the slope failure is considered to be caused by the liquefaction of foundation.
Cave-in 2
Although no damage to house or ground were observed outside the boundary along the survey line G –G’, the foundation settled by 60 cm at the inside of the boundary as indicated in Fig.6. This subsidence
at the inside of the boundary was considered to have occurred because the liquefied layer at the insideof the boundary moved mainly in the opposite direction to the boundary.
Photo 6 shows cave-ins along the survey line H – H’. As this is the view from north side, H’ and H
are located in the left and right sides of this figure, respectively. As seen in the figure, no foundation
damage was observed at the left (east) end of this figure, because that area was located in theunexcavated side. However, the severe cave-ins with several openings are observed in the excavatedside. This cave-in was considered to be caused by the movement of the liquefied soil in the excavatedside toward the opposite direction of the boundary.
Along the survey line I – I’, a main scarp whose height difference was about 1 m appeared at Point
I in Fig.6. Furthermore, several openings and gaps were created in the housing lot, resulting a total
subsidence of 170 cm in height along the line I - I’. A purified water tank of the sewage heaved up andmany traces of sand eject were observed in the neighboring yard. This cave-in was considered to becaused by the combined effect of landslide due to liquefaction of the foundation and movement of the
housing lot toward the opposite direction to the excavation boundary.

783

Shiinauchi area

Shiinauchi

Risen parking lot
and housing siteat the excavation
Excavation
boundary.
boundary

About
60㎝

Figure 7 shows the excavation boundary and the liquefied zone at Shiinauchi area. The apartment
house in Photo 7(a) was located at the inside of the excavated area and the road was located outside ofit. The apartment house undulated and deformed, and the parking lot heaved up by 60 cm, though nodamage was observed in the road. The dominant displacement direction of liquefied soil here isconsidered to be toward the road though the liquefied soil was hindered its movement by the stiff layer
under the road and heaved up. To the contrary, Figure 7(b) shows a cave-in occurred at the opposite
boundary in the Shiinauchi area. The foundation here was considered to have moved mainly toward
the opposite direction to the excavation boundary.

(a) Upheaval at north boundary(b) Cave-in at south boundary
Fig.7 Map of Shiinauchi area. Photo 7 Upheaval and cave-in at the inside of the excavation boundary
Time when liquefaction occurred
According to the results of interview to 28 victims, there are 5 houses where the sand spout wasobserved during and just after the main event started 14:46 on March 11 and 9 houses where it wasobserved the largest aftershock started 15:15, excluding 2 cases which were located on theunexcavated ground and 12 cases where the victims were absent during the events. This result wasdifferent from those at Mihama-ku, Chiba-city where all victims observed sand spout prior to thelargest aftershock, excluding unclear cases.

NUMERICAL INVESTIGATION OF OCCURRED LIQUEFACTION
Dynamic properties of liquefied sand
The intact samples were taken at the point, SWS 7, by penetrating short thin-wall samplers with alength of 25 cm into the sand layer after removing the surface soil with a thickness of 80 cm at the
middle step of the agricultural field shown in Fig.5. These samples are called “Hebizono”. Other intact
samples were taken below a depth of 80 cm in the same manner at Point F’ shown in Fig.6. Thesesamples are called “South of Shrine”. The liquefaction strength and the dynamic deformation
properties were shown in Fig.8 and Fig.9, respectively. According to Fig.8, liquefaction resistance ofthe soil at Hebizono is larger than that at South of Shrine.

784

Shearstress ratio σd /2σ0 ’
繰返し応力振幅比

0.3
Hebizono
蛇園（畑）
DA=5
u=95％

0.28

0.259

0.26
0.24

South
of shrine
浅間神社南
DA=5
u=95％
Simulation

0.231

0.22
0.2
0.18
1

10

100

1000

繰返し載荷回数
Numberof cycles Nc

Fig.8 Liquefaction strength of excavated and backfilled iron sand (Hebizono zone)

25

0.8

20

0.6

15

0.4

10

0.2

5

○

G/G0

1

30

0
1.0E-06h （％）

Simulated result
Experiment results△: Hysteresis damping ratio

1.2

0

1.0E-05

1.0E-04

1.0E-03

1.0E-02

Shear strain γ

Fig.9 Dynamic deformation properties of excavated and backfilled iron sand (Hebizono zone)
Outlines of two-dimensional fully-coupled dynamic effective stress analysis
Two-dimensional fully-coupled dynamic effective stress analysis software UWLC (Forum 8 Co. Ltd.
2005) was used in this paper. The software UWLC consists of three parts: (1) a program used to
identify the parameters of constitutive laws by simulating the laboratory tests, (2) a program tocalculate the initial effective stress before the earthquake, and (3) a fully-coupled dynamic effective
stress analysis program to calculate the seismic response. The derivation of finite element formulae on
the fully-coupled effective stress analysis was detailed in the Manual of UWLC. Rayleigh dampingwith a damping coefficient of 0.02 was also introduced. The time increment of 0.001 s was used.
Parameters for constitutive models
In this paper, the generalized plasticity model for sand developed by Pastor et al. (1990) and modified
in some aspects (Cai et al. 2002) was used for the excavated and backfilled iron sand, andHardin-Drnevich model was used for the unexcavated iron sand. The laboratory test results were used
to identify the parameters of the generalized plasticity model for the excavated and backfilled ironsand. The values of parameters were shown in the previous paper (Onoue et.al. 2012). As shown in Fig.
8, the simulated liquefaction strength using the identified parameters was consistent with thelaboratory results. The parameters of Hardin-Drnevich model for unexcavated iron sand were
determined using the dynamic deformation test results shown in Fig. 9, here initial shear stiffness G0
was estimated using N-value of the standard penetration test and a statistic equation.

785

Analyzed cross section and input motion
Cross section E-E’ proximately in the north-south direction was selected in the numerical investigation,
and Fig. 10 shows finite element mesh. The thickness of the analyzed ground was 8 m based on in-situ
investigation. The width of the left and right un-excavated grounds were respectively 100 m, and thewidth of the excavated and backfilled iron sand ground in the middle of the mesh was 200 m, of which
the upper soil layer 6m thick was excavated and backfilled iron sand and the lower soil layer 2m thick
was unexcavated layer. Points A and B located at a depth of 3m from the ground surface, thehorizontal distance from Point A to the excavation boundary was 8m, and Point B located at the
middle of the excavated and backfilled iron sand ground. The groundwater level was at a depth of 1m
below the ground surface.
Seismic wave at 14:26:00 of the main shock and at 15:15:00 of the largest aftershock in NS
direction observed at K-Net Yokaichiba station (CHB010) was used as input motion. Fig.11 shows theepicenters of the main shock and aftershock as well as the location of Asahi city. Because of the time
limit of numerical analysis, the time interval between the main shock and the largest aftershock was
shortened as shown in Fig. 12. Moreover, preliminary analysis was carried out to adjust the input
motion until the calculated maximum acceleration at the ground surface was consistent with theobservation.

Fig.10 Finite element mesh with a thickness of 8m
Numerical results
Figure 13 shows the time histories of excess pore water pressure ratio at points A and B. At Point A,
the excess pore water pressure ratio increased to 0.64 during the main shock and kept almost constantafter the main shock. It reached then 0.95 during the largest aftershock. In contrast, at Point B, themaximum excess pore water pressure ratio during the main shock reached 0.95, indicating almost
liquefaction. It lowered to 0.85 after the main shock and then increased once again to reach completeliquefaction. The numerical results support the testimonies of eyewitness that sand boiling occurred
during the main shock at some places and during the largest aftershock at other places.
15:08 M7.4
11:45 March 9,
M7.3

14:46
Main shock, M9
15:25 M7.5

Asahi city

15:15 Largest
after shock ,M7.7

Fig.11 Location of Asahi-city and epicenters786

Acc (m/s/s)

2
1
0
-1
-2
0

100

200

300

400

Time (s)Pore pressure ratio Pore pressure ratio

Fig.12 Input motion of main shock and the largest aftershock(t=0s corresponding to 14:47:06, t=250s to 15:15:00, 11 March, 2011)

1.0
0.8
0.6
0.4

Point A

0.2
0

0

100

200

400

300

1.0
0.8
0.6

Point B

0.4
0.2
0

0

100

200

300

400

Time (s)Fig.13 Time histories of excess pore water pressure ratio at points A and B shown in Fig.10

CONCLUSIONS
The reclaimed lands which were backfilled with discarded iron ore sand were liquefied at various
areas and many residential houses were severely damaged in Asahi-city, Chiba-prefecture, due to the2011 off the Pacific coast of Tohoku Earthquake. Among these areas, the detail investigations, such as
victim interview, soil investigation, land survey, etc., and the numerical analysis on the liquefaction
were carried out at Nakasone zone in Hebizono area. As a result, following conclusions were obtainedwith regard to damage to foundation.
1)
The backfilled sand having a thickness of 5 - 6 m was liquefied at the basin-like reclaimed
land of about 250 m in width and about 1 km in length. Along the periphery of the reclaimed land, theliquefied soil up-heaved when it displaced toward the excavation boundary and caved-in when it
displaced to the opposite direction to the boundary. In the case of slope, landslides often happen
accompanied by such upheaval or cave-in.

787

2)
According to the victim interviews, the number of witnesses who confirmed liquefaction bysand spout during and after the main event is larger than that of witness who confirmed it during andjust after the largest aftershock starting 29 minutes later. This is a different feature from the time ofliquefaction occurrence along the coast of Tokyo bay, such as Chiba city, where the liquefaction
occurred during the main event.
3)
It was confirmed analytically based on the wave record and the soil properties that there
might be two cases that the liquefaction occurred during the main event and that it occurred during thelargest aftershock.

REFERENCES
Cai F., Hagiwara T., Imamura S., Ugai K. (2002). “2D fully coupled liquefaction analysis of sandground under tank.” Proceedings of the 11th Japan Earthquake Engineering Symposium, pp.
819-824. (in Japanese)
Forum 8 Co. Ltd. (2005). “Finite element fully coupled dynamic effective stress analysis program(UWLC),” Electrical Manual, http://www.forum8.co.jp. (in Japanese)
Iioka town. (1981). “History of Iioka town” (in Japanese)
Japan Meteorological Agency (2011). About the 2011 off the Pacific coast of Tohoku Earthquake (the28th report), http://www.jma.go.jp/jma/press/1103/25b/kaisetsu201103251730.pdf (in Japanese)
Ministry of Land, Infrastructure, Transport and Tourism, Kanto Regional Development Bureau,
Japanese Geotechnical Society (2011). “Elucidation report on the actual situation of theliquefaction phenomenon in Kanto district due to the 2011 off the Pacific coast of Tohoku
Earthquake.” http://www.ktr.mlit.go.jp/ktr_content/content/000043569.pdf (in Japanese)Onoue A., Yasuda S., Toyota H., Inotsume T., Kiku H., Yamada S., Hosaka Y., Tsukamoto Y., Towhata
I., Wakai A. and Ugai K. (2011). ” Review of Topographic and Soil Conditions for
Liquefaction-Related Damage Induced by the 2007 Off Mid-Niigata Earthquake.” Soils andFondations, Vol.51, No.3, pp.533-548.
Onoue A., Cai F., Nakajima M., Nishikawa M., Torigoe T., and Yoneda K. (2012). “Behavior ofliquefied soil at brink of backfilled basin.” Japanese Geotechnical Journal, Special Edition for the2011 off the Pacific coast of Tohoku Earthquake (In Japanese, under review)
Pastor M., Zienkiewicz, OC., Chan AHC. (1990). “Generalized plasticity and the modeling of soil
behavior. “ Inter J. Numerical Analysis Method in Geomechanics 14, pp.151-190.

788