Engineering Geological and Geotechnical studies of Taprang landslide, west-central Nepal: An approach for slope stability analysis

Abstract

Detailed investigation of Taprang landslide was carried out in order to understand the surface, subsurface lithological information and physical properties of soil by using multi-disciplinary methods such as engineering geological, geophysical and geotechnical studies for the determination of factor of safety for slope stability analysis. Geological study was carried out by detail mapping of surface geology, soil condition, properties of bedrock and its discontinuities. The geophysical survey (Electrical Resistivity Tomography-ERT) were carried out to know the electrical resistivity of soil for identifying the groundwater table and hence slip surface of the landslide. Geotechnical analysis such as grain size analysis, liquid limit and direct shear test were carried out in order to evaluate soil classification, moisture content, cohesion and the angle of internal friction of soil for knowing the strength the soil. These soil parameters indicate the soil is very low strength. The combination of these results were used for calculating the factor of safety (FoS) by Limit Equilibrium Method (LEM) proposed by Bishop and Janbu methods. The result of factor of safety in the Taprang landslide demonstrates that the slope become stable in drained (dry) condition, remain ultimate stage in undrained (wet) condition and finally failure occurs if applied the seismic load in both drained and undrained conditions.