2019 Volume 25 Pages 669-674
In recent years, debris flow disasters associated with heavy rainfall have caused enormous damage. In order to reduce the damage caused by the debris flow disasters, it is an issue to clarify the slope failure mechanism focusing on the rainfall permeation process during heavy rainfall and to establish a prediction method based on the mechanism. So far, it has been pointed out that pipe flows under the mountain slope surface have a great influence on the occurrence of slope failure and debris flow. However, the conditions of pipe flow generation and how the pipe flows contribute to slope stability have many unexplained parts. This paper discusses the temporal changes in soil moisture and groundwater level with respect to rainfall based on the field observation data during the July 30 heavy rainfall. The observation site is Mt.Takamatsu, which was damaged in August 2014 by the Hiroshima heavy rain disaster. Field observations show that the groundwater level rises sharply during the heavy rainfall at the head of the slope failure. It is suggested that strong pore water pressure is induced by subsurface water in the deep part of the soil, which is considered to cause instability on the slope.
