Role of Geological Structures in Rock Slope Stability along a Road Corridor in Indian Himalaya

Abstract

Slope stability analysis is essential for sustainable development since rock slope failure can destroy infrastructure and road networks, threaten public safety, cause economic setbacks, etc. Slope failures are mainly confined to hilly terrain across the world. Himalayan mountain belt, the youngest and tectonically active mountain chain, is highly vulnerable to landslides due to complex lithological and structural variability. It requires a detailed field and laboratory investigation to understand the causes, mechanism and behaviour of slope failure. The main objective of this study is the detailed stability analysis of a rock slope located near North Almora Thrust (NAT) in the Pithoragarh district of Kumaun Himalaya along National Highway-09, Uttarakhand, India. The current study uses a multi-parametric approach which includes the kinematic analysis of slope, analysis of rock microstructures and their relation to meso-structures, the effect of microstructures on rock strength and geochemical analysis to understand the influence of mineral properties on rock strength. The stability of the slope was evaluated based on the limit equilibrium method (LEM) and finite equilibrium method (FEM). To imitate the actual field conditions, the slope model was simulated under static and dynamic settings for saturated and unsaturated conditions. The slope consists of intercalations of dolomitic limestone and phyllite with uniaxial compressive strength (UCS) of 55 MPa and 20 MPa, respectively. The Rock Mass Rating (RMR) of the rocks of the slope depicts that the rock mass quality is ‘poor’, and Slope Mass Rating (SMR) analysis illustrates that the slope is partially stable. Rock microstructural study discloses the development of strong foliation in the phyllite, which serves as the seepage for groundwater percolation. Therefore, an increase in pore pressure along these foliations can decrease the overall strength of the rock, inducing slope failure. The effect of the microstructure orientation on the rock strength was also examined for the slope. It was observed that an increase in the intensity of rock microstructures brought on a drop in rock strength. Shear sense indicators observed in the thin sections confirm the existence of the thrust zone. The slope stability analysis based on LEM and FEM revealed that the slope is critically stable in dry condition, but may  become unstable when considering dynamic and saturated conditions.Keywords: Himalayas, Slope stability, RMR, SMR, Geological Structure, Kinematic Analysis, LEM, FEM