Stability assessment of road-cut slopes along a section of NH-109 in Lesser Kumaun Himalaya, Uttarakhand, India

The changing and diverse nature of the environment presents challenges in predicting natural disasters, which are further exacerbated by human interventions such as road and dam constructions, tunnelling, and hydropower projects in mountainous regions, along with changing climate conditions. Landslides, common in mountainous terrain, pose risks to both travellers and residents. The susceptibility of mountain slopes to landslides increases during the monsoon season from June to September in the study area, as water infiltration saturates rock masses, increasing their weight and reducing friction angles. Additionally, the capacity of the drainage system to carry loads rises during this period. This study uses field-based data and various methodologies along the Bhowali–Lohali section of the National Highway-109 (NH-109) to assess slope stability and suggest landslide risk mitigation measures. A comparative analysis of slope stability was conducted using methods such as kinematic analysis, slope mass rating (SMR), continuous slope mass rating (CSMR), the chart method, and the landslide possibility index (LPI). According to the SMR, three locations (S3, S5, S7) are completely unstable, while only one location (S3) is completely unstable, according to the CSMR. Based on the LPI, two locations (S6, S9) have a very high possibility of failure, and the chart method indicates that four locations (S3, S4, S5, S8) are unstable. The study suggested necessary support systems such as rock bolting, shotcrete, wire meshing, ditch catchment and drainage systems at the suitability with site-specific in instability-prone localities to mitigate the landslide activities.