御岳土石流など不飽和土石流の流動機構について

Abstract

A big debris flow of 36 million m3 was caused by the Nagano Seibu earthquake at Mt.Ontake, 1983, in Japan. This debris flow seemed to be apparently different from the ordi-nary debris flow, because it looked to be not saturated.Then, the oppinion which this flow was a dry avalanche supported by pore air pressurewas presented in Newspapers & TV. Others insisted that it was an ordinary debris flow be-cause there can be no cause of such a high pore air pressure.This paper proposed the mechanism of unsaturated debris flow in use of the idea of un-drained shear of the saturated torrent deposit, which is analogus to the hydro-planing phe-nomenon in a rainy high way.