Rainfall induced slope failure detection using infiltration type slope stability method applying non-linear failure envelope

Abstract

Rainfall induced shallow slope failures in hilly terrain in the tropics is a complex soil mechanical behavior when it is difficult to be back analysed using the conventional slope stability method. The basis of the problem is in the applications of the linear soil shear strength failure envelope with cohesion intercept that over-estimate shear strength on the low stress levels i.e. for effective stresses less than 100 kPa or for failure depth less than 5 m. At this low stress levels the genuine shear strength behaviour is in fact non-linear with zero cohesion. Besides, the failure is not related to the groundwater table (GWT) when it is located at greater depth and has no influence on the failure. Theoretically the shallow slip failure surface is very difficult to be replicated with factor of safety (FOS) less than unity and that pose difficulties in understanding the failure. A slope stability method that deployed mechanics of unsaturated soils and calculate stability base on the advancement of the wetting front has been applied to characterize the shallow slips. The stability method uses the soil true non-linear soil shear strength behavior with respect to effective stress and suction. The method has been validated against a shallow slips triggered by rainwater infiltration that occurred along a road side in Cameron Highland, Malaysia.