Forensic investigation of roadside cut slope landslide in the lesser Himalayan region of Nepal

The failures in the roadside cut slopes in the Himalayan region are common events. However, the limited site-specific investigations often lead to reoccurring failures and escalating costs. This study attempts to critically examine a landslide along a national highway in Nepal’s Lesser Himalayas using a forensic geotechnical approach, providing insights that can be applied to similar terrains around the world. Assisted with the desk works and site visits, geophysical investigations were carried out employing Electrical Resistivity Tomography (ERT) combined with geotechnical investigation, boreholes drilling for the subsurface inspection and interpretation. The data collected from these studies were used to conduct slope stability analysis using Limit Equilibrium Method (LEM) based numerical modeling. The analysis showed an alarming low factor of safety (0.791 on the hillside and 0.799 on the valley side), primarily due to high groundwater table on the sand-dominant slope. These findings highlight the necessity for effective groundwater management and slope reinforcement for the mitigation of instability. This study aims to improve slope stability assessments and disaster resilience in landslide-prone areas around the world by showcasing a comprehensive investigation approach.