Strength evaluation of unsaturated slopes during heavy rainfalls and earthquakes

Hirofumi TOYOTA

Heavy rainfalls caused serious damage in Kyusyu area in 2003, and also in Niigata and Fukui in 2004. Moreover, many slope failures occurred at high groundwater areas of hilly and mountain regions during the 2004 Niigata-ken Chuetsu Earthquake. It is considered that those damages were expanded by rainfall before the earthquake. Although research focused on the groundwater level has been performed, little research where moisture state of soils is connected to the strength evaluation has been conducted. Especially, the stability of unsaturated slops should be estimated considering the moisture state of soils because those apparent cohesions vary with the degree of saturation. Therefore, experiments of unsaturated soils were carried out using samples obtained from dikes and natural slopes collapsed. The evaluation method on stability of unsaturated slops was demonstrated using those experimental results in this study.