Prediction of Stability of Hill Slope Through Electrical Resistivity Tomography

Landslides are very common events along NH 54, i.e., Silchar Halflong road. There are many sliding zones like Reko, Phiangpui, Muolhoi Digrik, Debarai, Nutan Basti, Mahadev tilla, Durbin Tilla, Synod turning, Tankaram turning, etc. where landslides occur almost every year. The state PWD removes debris every year with an assumption that the slides become stable and will not recur. No investigation has ever been done to evaluate the depth of the loose debris and the potential of future slides due to rains. In the present study, one potential slide area namely, Durbin tilla has been chosen for investigation. An electrical resistivity tomography (ERT) was conducted on the area during the winter season. Forty-eight numbers of electrodes at a spacing of 0.6 m center to the center were laid along the slope and electrical resistivity survey was conducted. It was observed that the top surface consists of loose gravelly sand of resistivity around 400 Ω m. Some pockets of loose boulders with high resistivity 3000 Ω m were also observed. High resistivity area near the top end of the slope was observed. The slope stability analysis was performed using GEO5 software using different methods like Bishop method, Sharma method and Spencer method. The possible slip surface and the factors of safety were determined in GEO5 software with the present groundwater table condition. It is observed that the slope is stable in its present condition but becomes unstable during rainy season due to rise in water table.