Investigating the role of geochemistry and geotechnical properties in landslide characterization and triggering mechanisms: a case study from dir upper, khyber pakhtunkhwa pakistan

The 83.5 km Chukyatan-Kumrat Upper Dir road plays a crucial role in transportation and tourism in North Pakistan. Despite its significance, the area faces frequent landslides due to hydrometeorological hazards, posing a threat to its stability. This study conducts the first extensive investigation of landslide susceptibility in the region, considering geological features, geotechnical properties, and rock weathering. The road traverses diverse rock formations, including meta-volcanics, andesites, meta-rhyolites, ignimbrites, volcanic ash, granodiorites, and spotted slates, overlain by residual soils. The presence of the Dir fault has led to significant accumulations of loose, weathered rock debris (>100 m deep). Exposed slopes exhibit polygonal stress fractures, joints, and fissures with steep inclinations (>40°), further enhancing instability. Geotechnical analysis reveals a low internal friction angle (28.5°-31.9°) and cohesion (4.1-5.9 kPa) of slope materials, indicating poor shear resistance compared to stable slopes. The unconfined compressive strength of bedrock (10.7-41.5 MPa) ranges from weak to moderate-strong, emphasizing the contribution of weaker rock formations to instability. Acidic soil pH (3.1-4.2) and clay minerals support the prevalence of weathering conditions promoting landslides. Thin section analysis and X-ray diffraction reveal hydrothermal alteration during low-grade metamorphism, leading to the formation of chlorite, smectite, montmorillonite, and zeolites. Additionally, physical weathering has increased quartz content, potentially impacting slope stability. The combined effect of factors such as steep slope geometry, low shear strength with strain-softening properties, rainfall, snowmelt, freeze-thaw activity, slope base cutting for road development, and massive loading from houses contributes to numerous landslides in the region. The study aids effective mitigation and preparedness in the Chukyatan-Kumrat area and offers insights for landslide susceptibility mapping in similar geological settings.