■Analysis of failure mechanics of the 2012 Kokugawa Landslide caused by snowmelt, Niigata Prefecture

摘要

Slope stability analyses are used in a wide variety of geotechnical engineering problems including not only the design of cut and fill slopes, and the stability evaluation of natural slopes, but also the analysis of past landslides to investigate failure mechanism. Several factors for the slope stability analysis, however, are uncertain and difficult to measure, especially the variations of shear strength parameter values of the cohesive soils and the variation of groundwater condition. The ring shear test apparatus is commonly used for obtaining the residual shear strength parameters. As the measured values of shear strength parameters are variable under the condition of shear rates and the different types of ring shear apparatus, the assessment and determination of these values are still difficult geotechnical problems. In this paper,in order to elucidate the failure mechanism of the Kokugawa landslide, firstly, ring shear tests are performed to investigate the residual shear strength of soils from the sliding surface and three pairs of the residual strength parameters are obtained ; Secondly, considering the variation of groundwater table, 3D stability analyses are carried out to confirm that which pair of cohesion and frictional angle can interpret the failure of the Kokugawa landslide ; Thirdly, the stress-strain behavior disturbed by the infiltration of snowmelt water in the slope of the Kokugawa landslide site is analyzed by Flac3D (Itasca software) program. The failure surface as indicated by the accumulation of shear strain zone is concordant with the sliding surface interpreted from the borehole logs.