Assessment of shear strength parameters and slope stability analysis of a landslide from Lesser Himalayan region of India

A landslide site, comprising debris underlain by jointed rock, from Lesser Himalayan region of Uttarakhand, India was considered for stability assessment. Shear strength parameters of the debris were obtained by performing direct shear tests using different shear box sizes. The variation of shear strength parameters with gravel content was investigated. Necessary rock mass strength parameters were determined by using Modified Mohr-Coulomb (MMC) failure criterion and rock mass rating classification systems (RMR) and Geological Strength Index (GSI). Slope mass rating (SMR) was used to categorize stability grade of the rock slope. Kinematic analysis was performed to check structural instability controlled by joints. For debris layer, stability analysis was performed by limit equilibrium approach. Parametric analysis was performed to account for uncertainty in gravel content for arriving at representative shear strength parameters of the debris material. The derived shear strength parameters were employed to perform stability analysis of the slope section for different combinations of saturation and seismic conditions. The results indicate that in dry state the slope remains stable, however pore water pressure due to incessant rainfall may induce instability and the slope becomes marginally stable. Based on the outcomes of the analysis, it is suggested that a good drainage system, support of rock mass at the toe of slope by RCC wall, and reinforcement of the rock mass using rock bolts can be used to enhance the stability of the slope.