Daisuke MIURA

Strength characteristics of unsaturated sandy soils under cyclic loading

Hirofumi TOYOTA

Serious damage occurred during the 2004 Niigata-ken Chuetsu Earthquake. A great number of collapses and landslides were generated by the earthquake in former Yamakoshi region, and five river-clogging landslides occurred in Imo River basin. It is thought that many slope failures occurred in the catchment area and that rainfall by Typhoon No.23 landed three days before the earthquake caused horrible slope collapses. The investigations after the earthquake have reported that sandy soils widely distributed in the collapse area. The degree of saturation is important factor because the rainfall and the geographical feature such as catchment area might cause slope failures. Therefore, the triaxial tests were conducted using the samples obtained form actual slope failure areas. In the experiments the real ground conditions was reproduced considering the degree of saturation.
The result of this research is shown as follows:
1.Internal friction angles of the samples are constant independent of disturbance and the degree of saturation.
2.When the undisturbed samples are making to unsaturated, their cohesions are constituted of apparent cohesion induced by unsaturation and cementation due to aging.
3.Strength decrease by cyclic loading in undisturbed samples is smaller than that in reconstituted ones because of cementation.
4.Strength decrease by cyclic loading in unsaturated samples is smaller than that in saturated ones because of apparent cohesion
5.Unsaturated sandy soils hardly cause strength decrease by cyclic loading except for the constant volume conditions.