Highway expansion and landslide susceptibility in the lesser himalaya: geospatial modelling and structural analysis along the Chamba–Sainj corridor

Abstract Landslides pose significant challenges to infrastructure development in mountainous regions, particularly along highways constructed in geologically fragile and tectonically sensitive terrains. This study examines the effect of road widening on the landslide susceptibility in the Chamba-Sainj corridor (NH-94 and NH-108) in Uttarkashi and Tehri districts, Uttarakhand. It can be observed from this study that the widening of highways plays a major role in changing the pattern of landslide susceptibility, especially in zones where slope failures are kinematically controlled due to the presence of structurally complicated areas. A temporal landslide inventory for 2012–2022 years was made in the buffer of the highway at 500 meters. Fourteen causative factors have been selected for making landslide susceptibility zonation maps based on three bivariate models viz frequency ratio, information value and shannon entropy (SE). The models’ effectiveness was measured through the value of area under the curve that was more than 90% in case of the pre-expansion and 85% for the post-expansion, showing that models performed well. Although slope stability showed improvement after expansion, high susceptibility (HS) and very HS (VHS) zones were highly concentrated in some critical sections. In the SE model, there was an increase of 6.21% in the VHS class mainly due to unstable slope cutting, poor drainage, and slope toe cutting. Kinematic analysis was done at 16 SMR values were notably lower at active failure sites, confirming the structural control on slope instability. This study highlights the significance of combining susceptibility models with outcrop-scale structural analysis to support sustainable infrastructure development and reduce geohazard risks in the himalayan region.