Identification of slip surfaces in shallow landslides at Aso volcano, Japan based on the fine fraction-plasticity index relationship

Abstract

Shallow landslides have frequently occurred in the Aso volcano, Kyushu island, Japan. Yet, observations of the effects of the physical properties of the soil on the landslide stratigraphy have not been explained. In this study, we conducted field observations—at two landslide sites in the Takadake mountain (Aso volcano) area—to identify the slip surfaces. We found that slip surfaces (at both sites) were located in the lower part of the N3-4 Kuroboku soil layer. This was determined by characteristics of the physical properties of the soil, including particle size distribution and plasticity index. Furthermore, we identified the relationship between plasticity index and the fine fraction of the soil to help explain the identification of slip surfaces. Results showed that Kuroboku and Scoria layers have different characteristics according to the plasticity chart (liquid limit-plasticity index relationship) as well as plasticity index-fine fraction relationship.