Satoshi Goto

Initial Trigger for Slope Failures in Volcanic Ash Layer of Hillside Surface in Izu-Oshima Island in Japan Due to a Typhoon Rainfall in 2013

In the year 2013, the typhoon Wipha passed through the neighbourhood of the Izu-Oshima Island from 15 to 16 October 2013, and on the early morning of 16 October, a large number of slope failures occurred at various sites in the island. The largest one occurred at a caldera external slope located in the western part of the island near Motomachi Town. In this study, the initial trigger for such huge failures in the upstream slope, as the beginning of this serious mud flood disaster, has been discussed in mechanical point of view. According to the results obtained from the experimental and analytical examinations including the centrifuge model tests, it can be concluded that the increase of the pore water pressure in the thin ash-fall deposits layer with high permeability has promoted the decrease of the effective confining pressure in the layer, and it caused the surface failures in the hillside slopes.