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

SOIL LIQUEFACTION OBSERVED AT AREAS
LOCATED ALONG THE LOWER STREAM OFTONEGAWA RIVER DURING 2011 GREAT EAST
JAPAN EARTHQUAKE
Yoshimichi TSUKAMOTO1, Shouhei KAWABE2, Takaji KOKUSHO3
and Kazuhiro ARAKI4
1Associate professor, Department of Civil Engineering, Tokyo University of Science,
Chiba, Japan, s-kawabe@rs.tus.ac.jp
2
Assistant professor, Department of Civil Engineering, Tokyo University of Science,Chiba, Japan, ytsoil@rs.noda.tus.ac.jp
3Professor, Department of Civil Engineering, Chuo University,Tokyo, Japan, kokusho@civil.chuo-u.ac.jp
4
Chemical Grouting, Co., Ltd., Japan, k-araki@tamacc.chuo-u.ac.jp

ABSTRACT: The earthquake reconnaissance investigations were conducted at someareas located along the lower stream of Tonegawa River, where the extensive soilliquefaction and associated phenomena were observed following the main shock of 2011
Great East Japan Earthquake of M = 9.0 that occurred at 14:46 on March 11, 2011, andalso the subsequent aftershocks. A series of Swedish weight sounding tests were carriedout at Hinode of Itako City and Fukashiba of Kamisu City, where widely spread soilliquefaction was observed. The soil profiles responsible for damages inflicted by soilliquefaction were demonstrated along with a help of SPT data, and discussed in detail.
Key Words: Great East Japan earthquake, Soil liquefaction, Swedish weight sounding
tests, Soil profiles, Tonegawa river

INTRODUCTION
Following the main shock of 2011 Great East Japan Earthquake of M = 9.0 that occurred at 14:46 onMarch 11, 2011, and also the subsequent aftershocks, soil liquefaction related damages to life lines,
infrastructures and residential houses were widely spread over various regions on Kanto plain, and“soil liquefaction” again has become one of the important issues for natural disaster mitigations andreductions, since 1964 Niigata Earthquake.
It is most noteworthy that tens of thousands of residential houses were subject toliquefaction-induced settlement and tilt over the ground surfaces covered by erupted sand boils locatedon reclaimed lands developed along Tokyo Bay, including some areas in Urayasu City and Chiba City.
The areas located along the lower stream of Tonegawa River were also found to be subject toextensive soil liquefaction, including some areas in Katori City of Chiba Prefecture and Itako City,731

Fig. 1

Location of Hinode of Itako City and Fukashiba of Kamisu City

Kamisu City and Kashima City of Ibaraki Prefecture.
The authors had some opportunities to conduct multiple series of field Swedish weight sounding
tests at Sawara of Katori City, Hinode of Itako City, and Fukashiba of Kamisu City, as shown in Fig. 1.
The results of the earthquake reconnaissance investigations conducted at Sawara of Katori City aredescribed in the accompanying paper by Kawabe et al. (2012). In the present study, the results of theearthquake reconnaissance investigations conducted at Hinode of Itako City and Fukashiba of Kamisu
City are described in what follows.

BACKGROUND
To understand the wide-spread occurrence of soil liquefaction at the lower stream of Tonegawa Riverduring 2011 Great East Japan Earthquake, it would be helpful to recognize the importance ofgeological history around this area.
In ancient history that just dates back to about one thousand years ago, there existed a large innersea, which was as large as current Tokyo Bay, around the areas including the current lower stream ofTonegawa River, and the old Tonegawa River used to run southwards on Kanto plain to pour into
Tokyo Bay, (Tonegawa River Lower Stream Office 2011). In Edo era of about four hundred years ago,in order to prevent floods at Edo, the old capital of Tokyo, caused by the old abraded Tonegawa River,the extensive civil engineering works were carried out, and the course of the river was purposely
deviated to run eastwards to flow directly into Pacific Ocean. The current stream of Tonegawa Riverwas laid down at that time. The completion of these extensive civil engineering works needed to wait
for about 60 years spanning from 1594 to 1654. Following the continued flow of the river water andthe gradual accumulation of loose river bed deposits, the sea water has progressively been replacedwith fresh water around this area, and a series of the currently seen inner lakes called “Kasumigaura”
have been formed. However, the abraded Tonegawa River relentlessly caused floods along its stream.
In Meiji era, a series of river works were carried out from 1900 to 1930, which can be divided into
three periods. In the first period from 1900 to 1909, the river improvement works consisting of river
bed excavations and river embankment constructions were conducted at the areas spanning from theestuary to the current Sawara district of Katori City, (Fig. 1). The river improvement works conductedduring the second and third periods covered the areas from Sawara to the upper reach of the river.
From a close look at the old map of 1880’s (TRLSO 2011) shown in Fig. 2, it is found that thecurrent district of Hinode of Itako City exactly coincides with the area forming an inner lake
connected with “Sotonasakaura”, as shown in Fig. 2. It is also found that current Wanigawa district,732

Fig. 2

Old map of 1880’s locating the current Hinode district of Itako City and Fukashima district ofKamisu City, (after TRLSO 2011), (Red lines indicate current waterside lines.)

corresponding to the triangle region immersed in the old Wanigawa River, was developed over old
swamp areas, and part of Fukashiba district was developed over possibly easily inundated paddy fields,with a help of reclamation by means of draining.

OVERVIEW
The authors had some opportunities to conduct earthquake reconnaissance investigations at Hinode ofItako City and Fukashiba of Kamisu City.
The acceleration records of the main shock at 14 : 47 were observed at nearby Kashima station ofK-Net, which is 308 km away from the epicenter, as shown in Fig. 3. The seismic shaking measuring
over 50 Gal continued for about 90 seconds, with the maximum acceleration of 658 Gal. The large
aftershock of M = 7.7, then struck the region at 15 : 13. The epicenter was off the coast of Ibaraki
Prefecture, which was 59 km away from Kashima station of K-Net, and the focal depth was 43 km.
The seismic shaking measuring over 50 Gal lasted again for about 100 seconds, with the maximum
acceleration of 408 Gal.
At Hinode district of Itako City, the wide-spread soil liquefaction caused settlement and tilt ofresidential houses, uplifted manholes and drifted sheet pile walls for water channels, tilt of manyelectric holes, and fractured surfaces of many roads covered by quite a huge amount of erupted sandboils, as apparently seen in Figs. 4, 5 and 6.
It was shown above that from a close look at the old map of 1880’s (TRLSO 2011), the current
district of Hinode of Itako City exactly coincides with the area forming an inner lake connected with
“Sotonasakaura”, (Fig. 2). From the aerial photograph of this area taken in 1947, this area had been
reclaimed by draining and had already been used as agricultural paddy fields, to cope with theshortage of foods experienced during that time. The reclamation by draining in Hinode district wascompleted in 1950, (Itako City HP). Since the development of nearby Kashima Coastal Industrial
Region was resumed in 1960’s, Hinode district of Itako City has become one of the areas chosen forresidential district development. The reclamation by means of seafloor sludge over the once paddy
fields was carried out during the period from 1970 to 1971. A series of construction works for waterdrainage, water supply and sewage, roads and bridges were then subsequently completed.

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Fig. 3Fig. 4

Acceleration records of the main shock observed at Kashima station of K-Net

Fractured and winding surface of roads,(Hinode of Itako City)

Fig. 6

Fig. 5

Post-liquefaction ground settlement and tilt,(Hinode of Itako City)

Uplifted and drifted sheet pile wall for water channel, (Hinode of Itako City)

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Fig. 7

Location of Hinode district of Itako City

It was also shown above that current Wanigawa and Fukashiba districts were developed over oldswamp areas and possibly easily inundated paddy fields, with a help of reclamation by means ofdraining. The triangle region immersed in the old Wanigawa River shown in Fig. 2 was reclaimed bydraining during the period from 1928 to 1933, and became called “Wanigawa” district, (Kamisu CityHP). It is also noteworthy here that there had existed quite a large number of gravel pits in Fukashiba
district. Since the groundwater level was high in this region, the underwater excavations for good
gravels and pebbles to some depths had been supposedly implemented primarily during the period
from 1960’s to 1980’s. Those gravel pits were then reclaimed by landfills originated from nearby
regions such as Omigawa of Katori City.

SITE INVESTIGATION AT HINODE OF ITAKO CITY
The current district of Hinode of Itako City is shown in Fig. 7. With a help of staff members of Itako
City, the authors have gained a good opportunity to conduct a series of Swedish weight sounding tests
at Hinode district on September 8 and 9, 2011. The locations of Swedish weight sounding tests areshown in Fig. 8. The details of Swedish weight sounding tests are described by Tsukamoto et al.
(2004) and Tsukamoto (2009).
Figure 9 shows the results of the field penetration tests, and the soil profile estimated along thecross section indicated in Fig. 8. One of the advantages in using static penetration tests such as
Swedish weight sounding tests, compared with dynamic penetration tests such as SPT, lies in the factthat they can easily detect weak thin strata, though they would not accompany sampling of soils withdepth and accurate monitoring of a ground water depth. In Fig. 9, it is seen that in the areas where theextensive soil liquefaction was observed, there existed a soil layer of what is estimated to be “oldreclaimed sand deposits” overlain by relatively new fills. It is also noteworthy that these areas areunderlain by a thicker layer of natural silt deposits. It is not clear if this thick natural silt deposit might
have affected the occurrence of soil liquefaction in this area.

SITE INVESTIGATION AT FUKASHIBA OF KAMISU CITY
Another series of Swedish weight sounding tests were carried out at Fukashiba district of Kamisu City735

Fig. 8Fig. 9Locations of Swedish weight sounding tests at Hinode district of Itako City

Results of Swedish weight sounding tests at Hinode district of Itako City (The ratios ofdistance to depth/height are not to scale.)with a help of staff members of Kamisu City on October 14 to 16, 2011. The shadow zones in Fig. 10
indicate the areas where the extensive soil liquefaction was observed. The circular zone that covers thecurrent Gohno-ike pond corresponds well to the area where the “old Gohno-ike pond” was located. It
is also seen that another shadow zone includes the area of reclamation on old swamp as well as paddy
fields, However it also extends towards inland. Figure 11 shows the locations of Swedish weightsounding tests conducted in the present study, denoted as ① to ⑩, whereas the SPT data available
are indicated in alphabetic symbols. In the areas containing the locations “G” and “B”, the thick layerof natural sand deposits can be identified, on which the reclaimed fills overlie. The locations of ② to
④ were positively identified as what had once been gravel pits and reclaimed with landfills, at which
the extensive soil liquefaction was also observed. In the areas further inland, there seemed to haveexisted quite a large number of gravel pits unidentified yet and reclaimed again with landfills.

CONCLUSIONSThe earthquake reconnaissance investigations were conducted at Hinode district of Itako City andFukashiba district of Kamisu City, where wide-spread extensive soil liquefaction was observed.

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Fig. 10

Fig. 12

Location of Fukashiba district of Kamisu City

Fig. 11

Locations of Swedish weightsounding tests

Results of Swedish weight sounding tests at Fukashiba district of Kamisu City (The ratios ofdistance to depth/height are not to scale.)

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Multiple series of Swedish weight sounding tests were carried out at these areas. From the results ofSwedish weight sounding tests, the subsurface soil profiles were estimated, and the soil layers
responsible for surface exposed damages inflicted by soil liquefaction were identified and discussed indetail.

ACKNOWLEDGMENTS

The authors would like to acknowledge Professor K. Ishihara for his continued support.
Thanks are also extended to the kind assistance from the staff members of Itako City andKamisu City. The boring data of SPT were obtained from Itako City and Kamisu City. Theacceleration records shown in the present study were obtained from K-Net database. The
financial assistances provided by J-Rapid of Japan Science and Technology Agency andGraduate School of Tokyo University of Science are also acknowledged. The Swedish weightsounding tests described in the present study were conducted with a help of R. Saito, R.
Takahashi, R. Kobayashi, K. Sakai, Y. Sato, H. Sato, Y. Saito and Y. Mimori.
REFERENCES
Itako City HP : http://www.city.itako.lg.jp/2400ai_pj/pdf/urban_planning/chapter_1.pdf
Kamisu City HP : http://www.pref.ibaraki.jp/nouson/toti/index.html
Kawabe, S., Tsukamoto, Y., Kokusho, T. and Takahashi, R. (2012) “Soil liquefaction observed atKatori City located along the lower stream of Tonegawa River during 2011 Great East JapanEarthquake”, Proceedings of One Year after 2011 Great East Japan Earthquake – International
Symposium on Engineering Lessons Learned from the Giant Earthquake.
Tonegawa River Lower Stream Office (2011) “Leaflets on Tonegawa River lower stream at thebeginning of Meiji era (No.1)”, Ministry of Land, Infrastructure and Transport, (in Japanese).
Tsukamoto,Y., Ishihara,K. and Sawada,S. (2004) “Correlation between penetration resistance ofSwedish weight sounding tests and SPT blow counts in sandy soils”, Soils and Foundations, Vol.44,No.3, 13 - 24.
Tsukamoto, Y. (2009) “Determining the undrained residual strength of soils from field penetration tests
with some case history studies”, Performance-Based Design in Earthquake GeotechnicalEngineering - from case history to practice – (eds. T. Kokusho, Y. Tsukamoto & M. Yoshimine),
CRC Press/Balkema : Theme Lecture, Proceedings of IS-Tokyo2009 (Tsukuba, Japan, June 15 – 18,2009), 179 – 192.

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