Slope stability analysis of Strawberry Hill Landslide and adjoining slopes along National Highway-5, Shimla, Northwestern Himalaya, India

Landslides are the major problem in the Himalayan region and cause severe socio-economic disturbances. In the hilly areas, roads are the worst affected part by the landslides. In this study, we conducted the slope stability analysis of Strawberry Hill Landslide and adjoining slopes near Malyana town along NH-5, Shimla using kinematic analysis, rock mass rating (RMR), and slope mass rating (SMR). National Highway-05 (NH-5) connects the remote districts of Kinnaur, Kullu of Himachal Pradesh, and the China border to the rest of the country and is important in terms of socio-economic as well as national security perspective. The route has been severely affected by the landslides in Shimla city as well as its nearby localities in the recent past. Kinematic analysis of joint data shows that rocks are prone to mainly wedge and planar failures. The RMR results show that the slopes belong to fair (class III) and weak (class IV) category. The SMR results for the slopes show that out of 12 slopes 7 slopes lie in the completely unstable (class V) category, 4 in the unstable (Class IV) category and 1 slope in the partially stable (class III) category. The factor of safety (FOS) was calculated for the slopes with the minimum SMR value using the fast-track method of friction-only charts for the wedge failure case. The results show that all the slopes are unstable with a FOS value of less than 1. We identified the highly unstable slopes along NH-5 due to the unfavourable orientation of the discontinuities. Human interventions and rainfall further aids to the triggering of the landslides. The possible remedial measures for the study area are anchored walls, gravity walls, systematic shotcrete, and deep drainage.