In-Situ Cyclic Direct Shear Tests on Volcanic Soil in the Site of Landslide Due to Earthquake

Abstract

Volcanic pumice soils are widely distributed in many countries. Mechanical properties of those need to be characterized since seismic ground motions can cause serious hazards such as large-scale slope failures and long-distance debris flows. Since volcanic pumice generally retains extremely high porosity and has a sensitive structure, the natural soil structure is easily broken during sampling or transportation. Therefore, it is preferable to conduct in-situ tests without disturbing the original structure of the soil. In this study, an in-situ direct shear test device was developed, and in-situ cyclic direct shear tests were performed on volcanic pumice (Ta-d). This pumice soil is considered to be the main cause of slope failure in Atsuma, Hokkaido, Japan, due to Easten Iburi earthquake in 2018. Laboratory direct shear tests were also conducted using undisturbed sample taken from the site. The results revealed that soil structure significantly affects shear strength. To evaluate the mechanical behavior of such sensitive soils, it is crucial to use specimens with as less disturbed specimens as possible. The newly developed in-situ direct shear test device was used to determine the cyclic shear strength of sensitive volcanic pumice soils.

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