1981 Volume 34 Issue 2 Pages 16-26
The danger index to forecast the outbreaking time of slope failures calculated from rainfall record has been searched and tested using two records of slope failures. One of the records is about slope failures in Kure City, Hiroshima Pref. reported by Fire Survice of Kure City. The other record is about slope failures in several prefectures, Hiroshima, Okayama, Yamaguchi and Ehime Pref. reported by the Ministry of Construction.
Attempts have been made to use the antecedent precipitation index and the storage amount of the Tank Model as a danger index of slope failures. These indexes are calculated from hourly rainfall record of the nearest observation station.
The best half life of the antecedent precipitation index for the forecasting of outbreaking condition is 24 hours. About the data of slope failures in Kure City (14 years, number of slope failures. 2690), 96 percent of the cases occured above the critical value, 55mm. The total period when the value of the index is greater than the critical value is about 90 hour/year under the weather condition of Kure. Slope failures occur in one hour out of 5 hours when the value of the index is above the critical value in Kure City.
These results show the antecedent precipitation index whose half life is 24 hours is available as a danger index to forecast slope failures. It is shown the storage amount of the Tank Model is also available as a danger index.
Using these indexes, the dangerous condition about 90 percent of the slope failures in Kure City can be pointed out more than one hour before the time of outbreaking. In this case, the dangerous period is about 90 hour/year.
The antecedent precipitation index with the same critical value in Kure City is available as the danger index of slope failures also about the records occured in each prefecture, Hiroshima, Okayama, Yamaguchi and Ehime.