ABSTRACT
This chapter deals with the landslide study at Sirwani, Sikkim and examines the influence of water on the safety factor by sensitivity analysis. The rock discontinuities were mapped along the landslide and road cutting exposures as per the norms of International Society of Rock Mechanics. The stability of slopes depends on the geological structures, geomechanical properties of the slope materials, groundwater/rainwater condition. The area near landslide consists of metamorphic arenaceous and argillaceous rocks intruded by basic sills that have been metamorphosed to epidiorite and talcose phyllites. The presence of rain/surface water may decrease the shear strength of the clays, so sensitivity analysis was done separately to determine the effect of water on factor of safety. The slope movements in the landslides involve a combination of earth slide and debris flow. The landslide is occurring mainly due to the formation of deep gullies and subsequent undercuts formed by the currents of uncontrolled flowing rainwater down the hill slope.
