Assessment of Geotechnical Properties in Landslide‐Affected Terrains: A Case Study From Solan District, Himachal Pradesh, India

ABSTRACT This study presents a geotechnical investigation of soil samples obtained from two landslide‐affected areas, Shamti and Kumarhatti, in the Indian state of Himachal Pradesh. These landslides were triggered during intense monsoon rainfall in 2023 (Shamti) and 2024 (Kumarhatti) along National Highway 5 (NH‐5). Rainfall analysis over the past three decades reveals that a combination of prolonged wetting and short, intense rainfall bursts was a primary cause of slope failures. Experimental investigations included the determination of the grain size distribution curve, Atterberg limits, moisture content, specific gravity, maximum dry density (MDD) and shear strengths of the soil samples obtained to characterise their physical and mechanical properties. It was observed that the soil samples at Shamti contain 91.2% sand, 6.4% silt and 2.4% clay, a plasticity index (PI) of 8.32%, MDD of 20.61 kN/m 3 , cohesion c ′ as 26.47 kPa, and friction angle φ ′ = 17.48°. The soil samples exhibited a low moisture content (~2%–3%) due to their dry‐season collection and coarse, sandy texture, which retains little water. They are classified as SP–SC (poorly graded sand with clay), indicating moderate plasticity and high sensitivity to moisture, making them vulnerable during heavy rainfall. In contrast, the soil samples at Kumarhatti comprise 86.6% sand, 7.4% silt and 6% clay, with a lower PI (3.27%), moderate MDD (17.46 kN/m 3 ), cohesion ( c ′ = 21.6 kPa) and friction angle ( φ ′ = 6.6°). It is classified as SM (silty sand), characterised by low plasticity and higher frictional strength, which makes the soil more stable than its clay‐rich counterparts. The results highlight the critical influence of soil texture, plasticity and moisture‐related behaviour on slope stability and landslide susceptibility of the area. These findings provide essential data to predict slope behaviour and develop effective slope management and mitigation strategies.