1659
Soil Properties of Liquefied Soils in Tokyo Bay Area by the 2011 Great East Japan
Earthquake
Propriétés des sols liquéfiés dans la baie de Tokyo pendant le grand séisme de l’Est du Japon en
2011
Yasuda S.
Department of Civil and Environmental Engineering, Tokyo Denki University, JAPAN
ABSTRACT: The 2011 Great East Japan Earthquake caused severe liquefaction in artificially reclaimed lands along Tokyo Bay.
These lands were constructed of soils dredged from the bottom of the bay. The dredged and filled soils were estimated to have been
liquefied by the earthquake, but their liquefaction strength was not so low because they contained much fines. The very long duration
of the main shock and an aftershock 29 minutes later should have induced the severe liquefaction. Two remarkable characteristics of
the liquefied grounds were observed: i) much boiled sand and large ground subsidence, and ii) the buckling of sidewalks and alleys.
The former must have occurred because the liquefied soils were very fine. The latter might have been induced by a kind of sloshing of
liquefied ground.
RÉSUMÉ : Le Grand Séisme de 2012, à l’Est du Japon a produit des nombreux cas de liquéfaction sévère des remblais artificiels, le
long de la baie de Tokyo. Ces terrains ont été construits à partir du compactage de matériaux dragués du fonds de la baie. Il était
connu que ces sols avaient une certaine susceptibilité à la liquéfaction. Cependant, leur résistance à la liquéfaction avait été estimée
comme supérieure, à cause de leur contenu important de fins, par rapport à celle qui s’est avérée réellement pendant le séisme. La
durée très longue du séisme principal et une réplique importante survenue 29 minutes après, apparaissent comme les causes de
l’ampleur de la liquéfaction. Deux particularités très évidentes ont été observées : i) Une quantité importante de sables a été éjectée à
la surface, avec des tassements considérables du terrain, et ii) La contorsion-roulement par compression des trottoirs et allées. Le
premier cas a peut être été le produit de la composition assez fine des sols et le deuxième cas par le « ballottement » du terrain
pendant le temps d’occurrence de la liquéfaction.
KEYWORDS: liquefaction, earthquake, sandy soil
1
INTRODUCTION
During the 2011 Great East Japan Earthquake, soil liquefaction
occurred in the Tohoku region of northeastern Japan and in the
Kanto region surrounding Tokyo because the earthquake was
huge, with a magnitude of Mw=9.0. Many houses, roads,
lifelines, and river dikes were severely damaged by soil
liquefaction. According to the Ministry of Land, Infrastructure,
Transport and Tourism (MLIT), about 27,000 wooden houses in
Japan were damaged due to liquefaction.
In the Tokyo Bay area, liquefaction occurred in a wide area
of reclaimed land along Tokyo Bay, though the epicentral
distance was very large, about 380 to 400 km. Large amounts of
boiled sand, large settlements and a kind of sloshing of liquefied
grounds were observed in the Tokyo Bay area. The author and
his colleagues conducted laboratory tests, model tests and
seismic response analyses to ascertain the properties of the
liquefied soils and explain the remarkable behavior of the
ground due to liquefaction.
Figure 1. Liquefied areas from Odaiba in Tokyo to Chiba (Kanto
Regional Development Bureau of MLITT)
2 EFFECT OF LONG DURATION OF SHAKING DURING
THE MAIN SHOCK AND AN AFTERSHOCK ON
LIQUEFACTION
2.1
Liquefied area in Tokyo Bay area
Figure 1 is a map of the liquefied zones in the Tokyo Bay area
(Kanto Regional Development Bureau of the Ministry of Land,
Infrastructure, Transport and Tourism, 2011). The ground
surface was covered with boiled sands all around the reclaimed
lands at Shinkiba in Tokyo, Urayasu City, Ichikawa City,
Narashino City and western Chiba City. On the contrary, sand
boils were observed only here and there on the reclaimed lands
at Odaiba, Shinonome, Tatsumi, Toyosu and Seishin in Tokyo
and at eastern Chiba City. The total liquefied area from Odaiba
to Chiba City reached about 41 km
2
.
Many houses, roads, and
lifelines were severely damaged in the liquefied zones. The
most serious damage was in Urayasu City, where soil liquefied
in about 85% of the city area.
2.2
Cyclic torsional tests to demonstrate the effect of the long
duration of shaking during the main shock and an
aftershock
The most remarkable characteristic of the liquefaction in the
Tokyo Bay area was that widespread serious liquefaction was
induced even though the recorded accelerations were not large
and the liquefaction strength of the reclaimed soils was not low.
Figure 2 shows ground surface accelerations measured by K-net
