Numerical investigation of the stability of landslide-affected slopes in Kerala, India, under extreme rainfall event

This study examines the stability and failure mechanisms of two landslide-affected slopes in Kerala, India, after an extreme rainfall event. The landslide was triggered by an extreme rainfall event that occurred between August 1st and 10(th), 2019. To analyze the landslide mechanism coupled flow deformation was employed in the numerical analysis. The necessity of performing coupled flow deformation analysis over the conventional saturation stability analysis was established by comparing the outcomes obtained from both methods with field observation. The coupled flow deformation finite element analyses were executed based on unsaturated soil mechanics, whereas in the elastic-plastic deformation analysis saturated slope failures below the groundwater table were assumed. The results of elastic-plastic deformation analysis suggested that the slopes were unstable when the water table reached the ground surface because of the rise in pore water pressure and consequent reduction in shear strength. The failure timing, zone of failure, and deformation pattern of the slopes predicted using coupled flow deformation analysis exactly matched with that observed at the field during and after the landslide. The results also showed that decreasing matric suction along the failure surface results in a drop in the safety factor of the slopes from 1.155 to 1.001 and 1.19 to 1.004. The outcomes of all the finite element-based analyses were compared with those calculated using infinite slope analysis, and the results were in good agreement. The results obtained in this article can be used to determine the maximum cumulative rainfall required to cause the slope failure in order to avert possible future disasters.