Harshita Bhardwaj, Mahesh Thakur
This study presents an integrated assessment of the Mandi Landslide, a debris slide that occurred on August 14, 2023, near the Old Suketi Bridge in Mandi district, Himachal Pradesh, following intense monsoonal rainfall. The research aims to examine the factors contributing to slope instability through field observations, geological and geotechnical investigations, and slope stability analyses. Observations indicated a steep slope angle (~ 60°), the presence of natural springs near the crown, and a jointed sandstone outcrop exposed along a road cut just outside the landslide body, near its left flank. Kinematic analysis of the exposed rock mass suggested the possibility of wedge failure under unfavorable conditions. Soil samples were classified as well-graded sand with clay (SW–SC) and were used to derive geotechnical input parameters for slope stability modeling. Pre-failure slope stability analysis using the finite element method (FEM) in RS2 software revealed a low strength reduction factor (SRF) of 0.49 and 0.39 under dry and vertical infiltration conditions, respectively. The SRF under dry conditions was validated by a factor of safety (FS) of 0.441 from Slide2 software. These findings highlight the role of rainfall-induced infiltration in reducing slope stability and emphasize the need for appropriate mitigation measures at the Mandi Landslide site.