Seismic shear behavior of clayey volcanic soil in residential area damaged by the 2016 Kumamoto earthquakes in Japan

Sandy volcanic soils, including pumice, are vulnerable to earthquakes. On the contrary, clayey soil does not liquefy and is stronger than sandy soil. However, during the 2016 Kumamoto earthquake, a large ground deformation occurred in the residential area of Mashiki Town wherein clayey volcanic soil was deposited. We studied the seismic shear behavior of this clayey volcanic soil using a torsional cyclic shear test with a random shear stress history corresponding to actual seismic records. In our test, we also studied the effects of a series of seismic motion histories and the initial shear stress because most damage occurred on the slope area. As a result, in the case with initial shear stress owing to the slope, a larger residual strain developed compared to the case without an initial shear stress.