Landslide stability assessment along Panchkula–Morni road, Nahan salient, NW Himalaya, India

Abstract

We report the slope stability analysis of three vulnerable sites (S1, S2 and S3) within the lower Siwalik along the Panchkula–Morni road section in the Nahan salient, north-western Himalaya. Kinematic analysis of joint data was conducted to understand the different modes of failure. Rock mass classification techniques like rock mass rating, slope mass rating (SMR) and continuous SMR were used for stability classification and the factor of safety was calculated using stability charts. At site S1, the instability is controlled by the orientation of the discontinuity joint J1 which is parallel to the bedding and at site S2, the slope fails due to the wedge. The Umri landslide site S3 is the product of a damage zone by the normal faults which intersect at joint J3; a wedge is formed which falls in the critical zone. The damage zone in the Umri landslide greatly affects the porosity and permeability of the rockmass and acts as a pathway for the percolation of water during rainfall which reduces effective stress. The slope failures are tectonically controlled results due to the high slope angles, structural discontinuities like joints and faults and structural damage zones associated with the faults.