2017 Volume 73 Issue 2 Pages 141-156
It is becoming progressively important to predict occurrence of slope failures induced by heavy rainfall because torrential rain and localized heavy rainfall are recently showing an increasing trend of occurrence. Prediction methods of slope failures are now required to make assessments from perspectives of not only for issuing warnings but also for canceling the warnings. In this study, an estimation method of in-slopes pore water pressure was considered as a quantitative criterion to determine when to cancel the warnings. The method first calculates Soil Water Index (SWI) from rainfall data using 3-series tank motels, and then applies a linear function to the calculated index in order to fit it equal to the maximum pore water pressure observed in field monitoring, and eventually estimates pore water pressure at which slopes start to collapse, on the basis of the fitting function used in the second process. The estimation method was applied to past rainfall histories recorded around several slope failure events in Izu Oshima Island for verification. The method successfully estimated and reproduced occurrence of surface failures which triggered debris flows in 1958 Typhoon Ida (the 22nd twenty of the year, also known as Kanogawa Typhoon) and 2013 Typhoon Wipha (26th typhoon of the year).