Field investigation and finite element modelling of a progressive debris slide in the Indian Himalayas

Abstract

The paper highlights the detailed field and laboratory investigation along with finite element modelling of a progressive debris slide along a highly vulnerable road stretch of Chamoli-Badrinath highway (NH-58) in Indian Himalayas. To investigate the failure process of the landslide, the slope was modelled along two different profiles using a finite element package PHASE 2 based on a 2-dimensional elastoplastic model for calculating stresses and displacements. The material properties for different layers on the slope were chosen from the laboratory test results of soil samples and available literature. Shear Strength Reduction (SSR) analysis was performed to determine the critical Strength Reduction Factor (SRF). It is observed that the critical SRF is 0.54 for left flank and 0.53 for right flank slope profiles. This indicates that the slope is highly unstable. The results show very good correlation with the observed field conditions. The locations of the landslide scars, from where the sliding processes have already been initiated, match exactly with the FE analysis result. The plane of sliding is observed to be the boundary between the bedrock and the highly weathered disintegrated dolomitic soil. A model to predict the progressive failure mechanism of the western flank of the landslide has also been attempted. After sliding of the material from the toe portion, the result of the FE analysis showed the probable location of 2 nd phase of detachment and with further sliding the final phase of detachment was obtained. The FE analysis results have also been validated with the field signatures. © 2012 WIT Press.