Investigation of Tombinoutek Landslide, Old Cachhar Road, Manipur, India

Abstract

The July 12, 2016 Tombinoutek landslide along state highway between Imphal and Jouzangtek village, Manipur, India affected the road section for a stretch of ∼475 m. The research aimed at finding the combined effects of topography, lithology and structural attributes of the landslide. Detailed geodetic survey was carried out using drone supported by ground control points obtained by total station survey. Base map with 5 m contour intervals, slope and aspect maps prepared; critical slope is between 45° to 60°. Geological studies have shown occurrence of intercalated sandstones and dissected shale, disturbed by five prominent joint sets which play an active role in the initiation of the landslide through plane and wedge failures. Geotechnical analyses of sandstones indicated strong compressive strength ranging between 80 and 97 Mpa, and tensile strength of sandstones and shales between 17 and 20 Mpa and 2.62 and 3.27 Mpa respectively. Soil analyses showed plasticity index (I_P, percentage) of 10.66, and liquid limit (W_L%) of 32.5. Average soil porosity is 80%. Liquidity index of -1.208 indicates relatively stable condition under dry condition. Plasticity index of 10.66 lies in the CL field, close to the boundary between low plasticity and medium plasticity. Sandstones show fair rock RMR with class IIb stable SMR, and shales show poor rock RMR with class IIIb partially stable SMR.