GEOTECHNICAL SIMULATION TEST FOR THE NIKAWA LANDSLIDE INDUCED BY JANUARY 17, 1995 HYOGOKEN-NAMBU EARTHQUAKE

FA-WU WANG , KYOJI SASSA and HIROSHI FUKUOKA

ABSTRACT By employing an undrained cyclic loading ring-shear apparatus, a series of tests to reproduce the dynamic behavior of the Nikawa landslide induced by the January 17, 1 995 Hyogoken-Nambu earthquake, is conducted. The test sample is Osaka-group coarse sandy soil taken from the landslide. The initial stress condition acting on a soil element in the sliding surface is applied to the sample. Based on the seismic records monitored at the JR Takarazuka Station, the input seismic wave is synthesized to reproduce the seismic stress acting on the sliding surface. The test results show that the soil failed due to the dynamic loading of the earthquake. The most important results are the excess pore water pressure generation and the acceleration of shear displacement continuing after the main shock. Combined with the grain crushing at the shear zone and the volume reduction in the drained constant-speed ring-shear test, the mechanism of this landslide is interpreted as, shear displacement causing grain crushing in the shear zone and volume reduction, and then resulting in a localized liquefaction phenomenon, "sliding-surface liquefaction". This geotechnical simulation test provides a reasonable interpretation of this highly mobile landslide.

Key words: excess pore water pressure, grain crushing , landslide, (localized) liquefaction, (ring-shear test), (seismic record), (simulation test) (IGC: E6/E8/D6)