Reconstruction of a wetting-induced shallow landslide in Shillong, India

Abstract

The hill slopes of the north eastern region of India often encounters shallow landslide during the rainy season. Forensic study of a failed hill-slope in such areas is useful in improving the understanding of the failure mechanism. An incessant rainfall triggered a shallow landslide in the Umshing Mawkynroh locality of Shillong in North-east India during the rainy season of 2019. In this work, a forensic investigation was carried out by performing a coupled unsteady-state seepage and stability modelling to reconstruct the actual failure surface. The recorded rainfall data, slope geology, and soil hydraulic properties of the compacted laterite soil were used to back-estimate accurately the in situ failure surface. The underlying mechanism responsible for the shallow landslide during the rainfall infiltration was identified from the numerical modelling. The combined effect of wetting front advancement in the initial partial saturation zone and the rise of the perched groundwater table was found to be the mechanism responsible for the failure.