An integrated geotechnical and geophysical investigation of a catastrophic landslide in the Northeast Himalayas of Pakistan

Landslides are a complex geohazard, and the key parameters that have a prominent effect on their nature are variations in slope angle and fluctuations in groundwater. The focus of this research was to analyse the prevailing conditions of the Danna-Sahotar landslide in the south of Muzaffarabad district, Sub-Himalayas, Pakistan, and evaluating how different conditions effect the stability of the landslide with the integration of geotechnical, geophysical, and slope stability analysis. The geotechnical investigations revealed that the surface layer is mainly sandy with clayey and silty content. The two-dimensional (2D) electrical resistivity tomography (ERT) demarcated the presence of a possible slip surface situated in the portion where the resistivity values clearly change. The ERT of the crown is characterized by low resistivity due to the presence of water seepages, which increase the degree of saturation and pore water pressure hence, leading to the slope failure. It was proved that the presence of high moisture content has played an influential role in triggering the landslide. Thorough analysis of integrated research yielded reliable and accurate information on the geotechnical and geological aspects of the landslide. The outcomes were used in slope stability limit equilibrium method (LEM) analysis using GeoStudio software. The slip surface predicted from the LEM was almost circular, which was confirmed by the geotechnical and ERT method. The factor of safety Fs (0.830) along the longitudinal profile of the landslide was calculated, indicating that the slopes along the profile are unstable. The geotechnical survey in combination with ERT and slope stability analysis helped to understand the failure mechanism of the landslide and to improve the layout of the future monitoring experiment, which may be used as a key for the observation of similar slope investigation.