Study of the Liquefaction History in a Lowland Area in Tokyo Caused By Three Earthquakes

Abstract eng:
On March 11, 2011, the Great East Japan Earthquake occurred, causing extensive soil liquefaction over a wide range of land in Japan, resulting in extensive damage to wooden houses, water supplies, and sewer systems. The damage caused by liquefaction also occurred in the bay coast of landfills in Tokyo, though liquefaction did not occur in the alluvial lowland area in the immediate vicinity of Tokyo Bay. In these alluvial lowlands, the district along the old Sumida River has been previously affected by liquefaction caused by earthquakes, including the Great Kanto Earthquake, 1923 and the Edo Earthquake, 1855. The reasons why the area was affected by liquefaction during the past earthquakes, but was not affected during the Great East Japan Earthquake can be considered by the following two factors: i) The ground had become unlikely to undergo liquefaction due to an “aging” effect, whereby the liquefaction strength of the soil gradually increased since the Great Kanto Earthquake occurred. ii) The area had not undergone liquefaction, because the ground motion of the Great East Japan Earthquake was weaker than the past two earthquakes. The tests were performed on the compacted specimen from one hour to a maximum of 100 days. Based on the results, the liquefaction strengths of the specimens that consolidated over longer periods of time were larger compared with specimens that were consolidated over shorter times. Also, the liquefaction strengths were observed to be relatively large in samples containing a larger amount of fine fraction material. The second part of the study examines the strength of the ground motion of the three earthquakes described in ii). In addition, soil data from liquefied areas during the past two earthquakes, changes in the liquefaction strength by the “aging” effect obtained from the test results in the first part of the study, and the magnitude of the earthquakes were used to determine why the area around the old Sumida River was not subjected to liquefaction. Based on the results, the area was not liquefied by the Great East Japan Earthquake in spite of the occurrence of liquefaction during the past two earthquakes because of the increases in the liquefaction strength due to the “aging” effect, as well as the presence of relatively small ground motions that occurred during the most recent earthquake event.

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