Analysis of Stability of Slopes in Himalayan Terrane Along National Highway: 109, India

Abstract

Morpho-dynamic terrane of Himalaya is continually facing challenges in stability of rock cut slopes, aggravated due to increased disturbance levels in rock/soil mass due to human intervention. Increased civil constructions, exploitation of resources, deforestation, changing pattern of river-flows and increase in population are among the key reasons for such disturbances leading to increased susceptibility of these slopes. Huge loss of property and lives has been reported every year from the Himalayan regions and therefore, must be attended on a priority basis. The lithological and structural variations, orientation and pattern of different water bodies and vegetation are varied along the slopes indicate site-specific studies of landslide prone areas for assessing the health of slopes and providing early warning, wherever necessary. Highly jointed rock mass along the slopes between Rudraprayag and Agasthyamuni along NH109, which connects to Indo-China border, the hilly population to the plains and runs parallel to River Alakananda, were studied. A detailed field study was carried out in the landslide area and the relevant geological data were recorded. The area constituted of mainly weak phyllitic and schistose rock at most of the places with some jointed and weathered quartzitic rock mass at a few locations. Stability of slope was investigated using two dimensional finite element methods. Slope geometry and rock parameters were incorporated in the models that were analysed for factor of safety. The changes in geomorphology as a consequence of surface and sub-surface deformations were also premeditated. At places, formation of weak tensile zones towards the rear end of the slopes as well as coalescence of schistose rock due to loading, indicate possible subsidence in weak areas, and may lead to changes in landforms. It is indicated that a stable slope in dry season may become hazardous in the wet season and remedial measures may be applied in advance to prevent any major damage to the ongoing traffic and other operations.