Landslide in fractured and stratified rocks: A case from Aizawl, Mizoram, India

摘要

Stratified rock cut slopes for e.g. shale-sandstone-siltstone layers are a common occurrence in some part of the Himalayas. These rocks are highly jointed and bears low strength to sustain significant engineering load. A similar geological condition exists in the north eastern Himalayas (Aizawl, Mizoram) where such rocks have been exposed along cut slopes. The area receives heavy rainfall during the monsoonal months and the presence of clay make these rocks highly susceptible to intense weathering. Further, the presence of widely spaced orthogonal joints along with persistent bedding parallel joints allow water to percolate deeper into the formation. Accumulation of water with time in the pore spaces of rocks and in the interface between the strata leads to opening of the joints and considerable reduction of shear strength. Despite of incompetency of these rocks, large number of transportation lines and settlements are being built to meet the demand of increasing population in India. Unscientific design and inadequate use of geological and geotechnical information during construction allow these rocks to deteriorate and degrade in strength before the engineering life of the structure eventually leading to slope failure and mass destruction. Therefore, the present study mainly deals with the influence of long term weathering on the strength degradation of the exposed rocks by a series of experimental observations followed by numerical simulation of cut slope using distinct element method. The purpose is to gauge into the health of the slope and the processes which leads to slope failure under normal gravity and hydro-mechanical loading conditions. The result of this analysis is very promising which discusses several important issues like effective loading direction, maximum allowed load on the crest of the slope, zones of maximum displacement and maximum flow rate observed along the slope face, mode and depth of failure plane. Understanding these challenges will assist the planners to design appropriate support systems for long term safety and sustainability of the structures and avoid future slope failure.