An assessment of Dungale landslide using remotely piloted aircraft system (RPAS), ground penetration radar (GPR), and Slide & RS2 Softwares

In the present study, slope stability analysis was done using limit equilibrium method and finite element method of the Dungale landslide situated in the NW Himalaya along Tons river. The data used for slope stability analysis was collected through geological and geotechnical field and laboratory-based studies. The field study includes remotely piloted aircraft system and ground penetration radar surveys, whereas laboratory study includes determination of engineering properties of slope forming material using standard methods. A road cut across the landslide often gets blocked during monsoon due to landslide reactivation. A fault has been identified running across the landslide at a height of ~ 76 m above the road from where continuous water flow is noticed, and above which instability occurred. The laboratory data reveals that the soil collected from the top of the landslide site is impermeable in nature and thus, may not uphold the flow of water into deeper horizons. Based on our investigation, we conclude that the landslide occurred in two phases. In the first phase, there is development and opening of the cracks in the uppermost layer of the soil at the top of the slope. Due to highly impermeable nature of the slope material, the upper topmost layer becomes saturated in the monsoon, and the inner layer within is dry. The differential water content exerts pressure within the soil and causes the opening of the cracks. In the second phase, the excessive flow of underground water during monsoon along the fault plane erodes the material at rock-soil interface causing the failure of the material. The slope stability analysis also confirms the limiting factors of safety during unsaturated state of soil, which lowers during saturated conditions.