Failure Mechanism of an Unsaturated Slope in the Nilgiris District, Tamil Nadu, India

Landslides are one of the natural disasters that cause an enormous amount of loss to both the individual and society. The Nilgiris in the Western Ghats are highly vulnerable to landslides where the triggering factor is rainfall. Around 76% of landslides occur due to rainfall. The failure mechanism of an unsaturated soil slope is presented in this article. The soil samples were collected from the Nilgiris location, where a landslide already occurred in 2009. Direct shear tests were performed to attain the shear strength parameters of the silty sand. The effect of infiltration on the unsaturated slope was analysed using coupled stress/pore water pressure analysis from SIGMA/W. The stability of the slope was analysed using SLOPE/W software. The results show that the safety factor is not constant throughout rainfall period, as done in conventional methods, and it varies depending on the period of infiltration and the matric suction of the soil. This analysis provides a realistic approach to calculating the factor of safety when compared with the other conservative methods.