Geotechnical and micro-structural characteristics of phyllite derived soil; implications for slope stability, Lesser Himalaya, Uttarakhand, India

Abstract Collapses of hill slopes along critical roadways are of dire consequence. Large literature is available on the stability assessment of hill slopes composed of rock and soils; however, a lacuna exists when it comes to geotechnical appraisal and instability aspects of slopes composed of in-situ saprolitic soils. The present study examines the physical, micro-structural and geotechnical characteristics of soil derived phyllite, and its ensuing influence on the instability of hill slopes at certain sections along National Highway-7, Uttarakhand, India. Four distinct locations along the highway were selected for the study. After field survey, the laboratory investigation was carried out to ascertain the geotechnical, chemical and mirco-structural parameters of the representative phyllitic soil samples. Eventually, stability analysis was carried out using Limit Equilibrium Method, Finite Element Method, and Finite Difference method, for the four locations. The analysis for location 2 & 4 showed them to be in a critical - unstable state, whereas, location 1 & 3 demonstrated stability in the present state. Compared to other techniques, FDM analysis results were in close congruence with the ground truth. The present study also sheds significant insight into the composition and deformation behaviour of the soils derived from the weathering of phyllite. The research may have enormous ramifications for the future assessment of similar soils and their possible use as admixtures in construction industry.