Study on a failed dip slope with a thin sandy layer in 2004 Niigata-ken Chuetsu Earthquake

Among the extensive failed slopes in the 2004 Niigata-ken Chuetsu Earthquake, Japan, a dip slope at Yokowatashi, Ojiya, was investigated intensively. The sliding plane was along a weak thin tuff sandy layer which had been deeply weathered. Triaxial compression tests and plane strain compression tests were performed on undisturbed specimens obtained by block sampling and boring sampling to evaluate the strength that was mobilized on the sliding plane. Stability analysis based on the test results reveals that, at normal time, without earthquake and without an extremely high groundwater level, the slope is stable. Furthermore, the calculation of earthquake-induced displacement provides a reasonable simulation of the failure of this slope.