阪神・淡路大震災-防災研究への取り組み-地震による都市域地盤の崩壊と災害の巨大化

Abstract

Distribution and types of ground failures due to the 1995.1.17 Hyogoken-Nanbu earthquake were firstly reviewed. A landslide (1.1-1.2 x 10^5m^3) in the Nikawa area, Nishinomiya city destroyed eleven houses and killed 34 persons. This landslide took place in a densely built-up residential area between Kobe and Osaka and it gave a shock to citizens who are forced to live near/in slopes in Japan. The mechanism of this landslide was investigated using a new cyclic loading ring shear apparatus which was developed in the Disaster Prevention Research Institute, Kyoto University to reproduce stress and motion in the sliding surface of earthquake induced landslides. This study revealed a new mechanism of rapid landslide, that is the 'Sliding Surface Liquefaction' caused by grain crushing along the sliding surface. The ground failure disaster was magnified by the rapid and long run-out motion of failed mass and the existence of densely built-up houses near/in slopes. Based on this study, the following four conditions for the identification of slopes causing catastrophic landslides during earthquakes were proposed;(1) slopes having a usually or often saturated layer(2) slopes consisting of soils subjected to grain crushing during shearing(3) Slopes having a much greater gradient than the apparent friction angle during motion of the soils(4) Existence of densely built-up houses within the landslide moving area.