Structure of slip surface in the Yachi landslide consisting of Neogene siliceous mudstone

Abstract

The objective of this research is to clarify the structure of the slip surface in Miocene siliceous mudstones where rock slidesoccurred frequently. In this research, test pit observations, soil tests, surveys of the slip surface using pipe strain gauges andtopographical analyses were conducted at the Yachi landslide, alarge-scale active landslide in northeast Japan. As a result, itwas found that the slip surface is formed in thetuff layers with lowest residual strength sandwiched between themudstones. It was also shown that the slip surface is discontinuous at the locations of depressions and tension cracks. At the toepart, it is also discontinuous and heterogeneous with an imbricated structure. Consequently, the behavior of groundwater flow is also affected by such discontinuous structure of the slip surface. Inaddition to clarifying the structure of the slip surface wherelandslides occurred in siliceous mudstone, the results of thisstudy will also be helpful for slip surface investigation, analysis of groundwater infiltration in landslide areas and planning ofgroundwater drainage works.