Structural Controls on Rock Slope Instability in the Bhotekoshi Corridor, Sindhupalchowk, Nepal, Following the 2015 Gorkha Earthquake

Abstract

This study critically examines the post-earthquake stability of a mountain slope in the Bhotekoshi Hydropower area, Sindhupalchowk District, one of the regions most affected by the 2015 Gorkha Earthquake of Mw 7.8. The weak geological formations of the area and steep terrain have repeatedly triggered slope failures, damaging highways, hydropower structures, and settlements along the Araniko Highway connecting Kathmandu to Tibet. Using Slope Mass Rating (SMR) and Stereographic Projection techniques, the study identifies key discontinuities, notably at 235°/67°, that control slope instability. The obtained RMR (27) and SMR (37.8) classify the slope as Class IV (Bad), denoting high instability and potential for large-scale planar and wedge failures. Stereographic analysis indicates that 57% and 28% of the area are critically prone to planar and wedge failures, respectively. These findings reveal significant structural weaknesses and emphasize the urgent need for systematic stabilization and continuous monitoring to safeguard hydropower infrastructure and communities in this seismically and geologically fragile region.