2022 Volume 95 Issue 2 Pages 123-137
Immunity to slope failure is based on the concept that once failure occurs, it does not recur until the soil layer recovers. It is worth examining whether two slope failures occurred on the same slope to verify whether that immunity is maintained during a certain period. The aim of this study was to reveal the distribution of slope failures induced by the Makurazaki typhoon and to verify whether slope failure immunity was maintained between the Makurazaki typhoon and 2018 heavy rainfall.
Based on the interpretation of aerial photographs, 3,787 slope failures were induced by the Makurazaki typhoon. It is believed that the occurrence of slope failures and amount of precipitation may be related. Areas of high slope failure density overlapped during both the Makurazaki typhoon and 2018 heavy rainfall. Thus, either immunity does not exist or the effective period is shorter than 73 years on a mountain or watershed scale. However, 113 slope failures were caused by the 2018 heavy rainfall on the same slope where failure occurred with the Makurazaki typhoon, and the recurrence rate was only 1.4% of total slope failures. In addition, the length of slope failure caused by the 2018 heavy rainfall on the same slope where it occurred due to the Makurazaki typhoon was shorter. These results suggest that the surface soil where slope failure occurred with the Makurazaki typhoon did not recover sufficiently during the period of 73 years up to the 2018 heavy rainfall, and that the immunity to slope failure was maintained.
Geographical Review of Japa,. Ser. A, Chirigaku Hyoron
