EVALUATION OF RUN-OUT DISTANCES OF SLOPE FAILURES DURING 2004 NIIGATA-KEN CHUETSU EARTHQUAKE

摘要

References(9) During 2004 Niigata-ken Chuetsu Earthquake in Japan, a large number of landslides occurred on natural slopes, especially at the hillsides in the region of Yamakoshi. In many of the large slides, the debris has travelled through a fairly long distance, aggravating the disaster caused by the landslides. In recognizing its importance, case studies were undertaken on the run-out distance of the landslides at several sites at Higashi-Takezawa, Mushigame and Naraki. Case studies are also undertaken for slope failures involving the man-made deposits behind retaining walls surrounding the residential hill at Takamachi-Danchi in Nagaoka. In the first section of the present study, a simple analytical method is introduced based on the energy principle, in which the residual strength is taken up as a sole parameter to determine the run-out distance combined with the geometry of the landslides. The slope failure is herein assumed to consist of two phases, sliding and spreading, and the sliding distance is defined as the length of a slope on which the mass of soils slides down, and the run-out distance is determined as the one on a gentle slope or flat plane on which the phase of spreading occurs. Soil samples were retrieved from the sites of landslide, and laboratory triaxial tests are conducted on unsaturated soil samples with varying water contents. The residual shear strength thus obtained was used as an input parameter in the simple analysis to forecast the run-out distance. The outcome of the present study is presented in a form of simple charts in which the run-out distance is expressed as function of relevant geometrical parameters and the residual shear strength of soils involved in the landslide.