Risk chart for identification of potential landslide due to the presence of residual soil

The incidence of slope failure involving residual soils in the Himalayan Region has increased in recent times. The prevalence of subtropical climatic zone has led to rampant weathering of varying degrees, resulting in the occurrence of residual soil over the bedrock. The study aims to give an overview of residual soil and its effect on the overall stability of the slope. Finite element-based numerical simulations have been performed utilising the results form field visits, laboratory experiments and detailed literature survey, and a landslide risk chart has been proposed. The results indicate the significance of considering the residual soil layer while performing stability analysis. A substantial decline in the factor of safety (FOS) was observed with an increase in the depth of soil layer up to 4 m, and a further reduction in FOS is not observed beyond this depth. Simulation results also indicate limited possibilities of the presence of a thick layer of residual soil on slopes greater than 45°, which is also established through field study. The overall stability of a slope depends on the critical combination of slope inclination, slope height and depth of residual soil layer. The proposed risk chart can be utilised for quick identification of vulnerable slope profiles, thereby indicating priorities for landslide risk management.