Geological and geotechnical investigations of the Sataun landslide along the Active Sirmauri Tal Fault, Sataun, Northwestern Himalaya, India.

In the present study, the Sataun landslide was investigated along the National Highway-72 (NH-72) between Sirmauri Tal and Sataun towns of the Sirmaur district of Himachal Pradesh, Northwestern Himalaya, India. Geologically, the Sataun landslide is composed of Middle Siwalik sandstones, which are highly fractured and faulted due to the interaction of the active Sirmauri Tal Fault zone and the Malgi Fault at the site of the Sataun landslide. Through the geological field investigations, three unstable zones were identified, which are prone to landslides. A major failure along one of the unstable zones (Sataun landslide, Zone 1) occurred on the 9th of October 2019. The investigation of the Sataun landslide was carried out using geological, geomorphological, geotechnical, and kinematic analysis. A pre-landslide topography was used to analyse the slope stability using FEM (finite element modelling) technique. Geomorphological studies and field investigations suggest the presence of an active fault zone (Sirmauri Tal Fault zone) passing through the Sataun landslide zone. Grain size analysis demonstrates that the soil is non-cohesive poorly graded sandy soil and geotechnical parameters indicate low cohesion (0.17 kPa) and low angle of internal friction (33.09°). Pre-landslide slope modelling suggests a low factor of safety (0.76). Toe cutting by the Giri River, the presence of radial, transverse cracks on the landslide body, and tension cracks on the crown propose the active and progressive nature of the landslide. Although the role of active fault is the most crucial factor for the Sataun landslide failure, rainfall played a critical triggering role in the Sataun landslide. This study shows that the unstable condition of the Sataun landslide may trigger another event of similar or greater intensity in the near future; therefore, proper monitoring is required to mitigate this landslide. [ABSTRACT FROM AUTHOR]