Geological reports of Shimane University

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Geological reports of Shimane University 3
1984-06-30 発行


Slope failure caused by heavy rainfall of July, 1983, in the west region og San'in District
Wada, Masayuki
Inamoto, Akira
Nagata, Jitsuya
An occation of the slope failure in this time is due to the heavy rainfall of Baiu front. However, the forms of slope failure are separated into several types under the topographic and geol ogi c condi t i ons.
Results obtained from auther’s investigation are as follows;
1)The slope failure are causedbyheavy rainfan with ma, ximum intensity reaching 96mm per hour and 372mm per day.
2)The topographic feature in this region is characterised by the wide spread hilly terrain. The summit level of hills are separated into four levels and monadnochs. Four levels consist of one river terrace, and three peneplanes which are "Takatsumen" at a height of 70-100meters, "Iwamikogenmen" at a height of 200-300 meters and "Takauchimen" at a height of 350-420 meters. The river terraces are the place safe from slope failures. A number of slope failures occurred on the steep slope of the Takatsumen side. There are underlained by post Miocene conglomerate, Miocene mudstone and muddy schist of "Sangun" metamorphic group, and the conglomerate unconformably overlies the other rocks. A large scale of slope failure occurred in these condition. Few slope failure occurred on the Iwamikogenmen. However, a large scale of debris flow occurred on the Iwamikogenmen around the monadnoch. A number of large scale of slope failure occurred on the monadnoch where are underlained by dioritic rocks weathered to red soil.
3)The most of large scale of slope failure occurred on the place with slope failure in old time, and the slope with old cracks and fissurs.
4)The disaster prevention works are composed of the countermeasures to hazards of the slope failure and debris flow, firming of crack zone by the anchor bolt method, observation of the change in slope feature, detection of the change of water conditions in the waming system, and evacuating to the refuge in early times.