Stability analysis of road-cut slopes (NH-3) under unsaturated and saturated conditions

Road-cut slopes along the highway in the Himalayan region are prone to rainfall-induced slope failures, especially during the monsoon. Nevertheless, most of the previous studies on slope stability analysis have been carried out using conventional methods where just one approach and one hydrologic state have been considered. Slope failures occur frequently along the National Highway (NH)-03 between Aut and Manali in the Beas Valley, Himachal Pradesh, highlighting the need for a more sophisticated stability analysis of the slopes. This study focuses on the slope failure process and evaluates the effect of the change in moisture content of the rock mass from unsaturated to saturated states. Four critical slope failure zones were studied with an integrated approach comprising kinematic analysis, geological strength index characterisation, the limit equilibrium method and the finite-difference method. Kinematic analysis suggests that wedge failure is the primary mode of failure, and planar failure is also possible in certain regions. The stability studies reveal that the factor of safety is higher in unsaturated conditions, while in saturated conditions, there is a decrease in the factor of safety by 21–32%. The findings revealed that a critical condition of instability prevailed during the initial period of rainfall infiltration.