Instability analyses of Merhülietsa slide, Kohima, Nagaland

摘要

Part of Merhülietsa colony of Kohima town and the national highway passing through it was devastated by a landslide on May 13, 2007. This unstable zone affected by rotational failure lies in the Disang sediments comprising shale with intercalations between thin-bedded siltstone and fine-grained sandstone. The shales are sheared, crumpled, and weathered to a high degree. This is attributed to a strike-slip fault and two shear fractures. Geotechnical analysis was carried out in the area and a factor of safety of 0.60 obtained for the slide mass. Similar work is extended to the surrounding area which had developed tension fractures. A slip circle drawn from tension cracks helps define future failure planes. A factor of safety of 0.93 is obtained indicating the possibility of progression of the slide zone. Rock mass rating of the shales surrounding the slide zone indicates poor rock condition, pointing to danger of collapse with further progression of the slide zone.