Appraisal of a Complex Landslide at KohimaTown, Nagaland, India

The interplay between geological and geomorphic conditions, moisture significantly influence landslide occurrences, though their precise relationships are often inadequately defined. This study aims to elucidate the factors affecting landslide activity in the Tarliedzü area of Kohima town. The area has experienced surface instabilities very frequently for the last three decades disrupting traffic and causing severe hardships to many towns and villages of Nagaland. Several attempts to stabilize this chronic landslide by simple rock and soil fill in the depressed portions, erecting gabion, and retaining walls have failed to arrest the problem. The difficulty in finding a permanent solution stems from the fact that several geological factors are at play in tandem, hence making it a complex slide, which requires a pragmatic mitigation approach based on the findings of a multi-disciplinary approach. A comprehensive, multi-parameter analysis was therefore conducted, incorporating geological and geotechnical, kinematic studies, joint analyses, and resistivity surveys to identify the underlying causes of the landslides. The area consists of fractured shales and weathered layers with high water concentrations. Structurally, the rocks are intersected by 3-4 joint sets, which are well illustrated by rose diagrams and stereographic projections. These joints are responsible for a wedge or planar failure in these rocks. While geological discontinuities such as joints are critical contributors to slope instability, the inherent weakness of slope materials has further exacerbated the problem. High groundwater levels, as indicated in dug wells, also point to the saturation of subsurface materials, thereby accelerating the weathering of these weakened formations. Keywords: Landslide, Kohima, Geotechnical Analyses, Kinematic Analyses, Resistivity Survey, Groundwater