Investigating the role of geological strength index and susceptible zones in landslide triggering mechanisms from Chukyatan-Kumrat road, Dir Upper, Pakistan

Abstract This study presents a comprehensive investigation of landslide susceptibility along the 83.5-km Chukyatan-Kumrat road, Upper Dir, North Pakistan. Despite its critical role in transportation and tourism, the region faces recurrent landslides due to hydrometeorological hazards, posing significant threats to stability. Employing a multidisciplinary approach, this study integrates the geological strength index (GSI) calculated from joint analysis of bedrock and landslide susceptibility index (LSI) analysis to understand the complex interactions underlying landslide occurrences. The study area contains a variety of rock formations, including metavolcanic, andesite, metarhyolite, igneous rocks, volcanic limestones, granodiorites, and spotted slates, which are overlain by remnant soils. Utilizing the landslide susceptibility index (LSI) map developed via the frequency ratio technique, regions proximal to road cuts, fault lines, and mineralogically altered and sheared lithology are identified as highly susceptible to future sliding events. GSI and rock mass rating (RMR) analyses categorized jointed bed rocks into relatively stable (zones 1 and 2; GSI 66–59, RMR classes II and III) and sheared and altered (zones 3 and 4; GSI 37–15, RMR class IV) segments, highlighting their differing susceptibilities. These zones have a moderately to highly weathered, slicken-sided jointed structure that allows rainwater and snow to infiltrate. The alteration mechanism of minerals such as chlorite, biotite, amphibole and alkali feldspar, as well as the influence of freeze–thaw cycles and precipitation on the pores and joints of bedrock, further weaken the rock, and there is a serious risk of landslide. This research contributes to the development of effective natural disaster mitigation and preparedness measures in the Chukyatan-Kumrat region. This study provides valuable insights for mapping landslide vulnerability in similar geological settings.