The Evaluation of Hydrological Impact through Temporal Resistivity Investigation at Lantakhola Landslide Area, North District, Sikkim Himalaya

Lantakhola landslide area of North district in Sikkim Himalaya has origin through cloud-burst in 1965 with it’s continuation at present. It possesses instability circumstance to National Sikkim Highway [NSH] due to prevailing adverse hydrological impact. The rainfall of high intensity with large magnitude during each monsoon period leads to continuous easterly shifting pattern of crown portion towards top of hill range. The surface water as three active stream channels with their turbulent flow encourage charging of sediments, losing their shear strength and vibration due to cyclic load of traffic movement on NSH provoke liquefaction among soil. The enormous high recharge condition of groundwater has been due to presence of tensional- cracks, weak geological plane, foliation plane along steeply slope on account of the regional central Himalayan thrust, passing through area advocates excessive positive groundwater pore pressure. Temporal Resistivity investigation along 19 instrumentation sites has been carried out during successive pre-monsoon, monsoon,& post-monsoon period along five major portions of Lantakhola landslide area namely: Crown, Central along NSH, Southern NSH, Northern NSH& Toe. The objective of study has been to decipher the groundwater disposition in major part of area, role of water in it’s different form during various seasons and the status of hard rock occurrence at subsurface, with factual information for pillar/ foundation of proposed Cantilever bridge construction.