Investigation of ground fissures at Kausaltar, Kathmandu by in-situ testing and spatial geographical mapping

Abstract

On April 25th, 2015, the Gorkha earthquake jolted the central region of Nepal, causing extensive damage to buildings and grounds in the urban areas of Nepal. One embankment section of Kathmandu-Bhaktapur Road, crosses a small valley in the center of the Kathmandu Basin. The earthquake has caused this embankment to deform with its supporting soil. Investigating the mechanism of this ground deformation from the geotechnical and geological viewpoints was deemed necessary to examine possible countermeasures. For this purpose, we conduct several in-situ tests such as microtremor measurements, standard penetration tests, and Multichannel Analysis of Surface Waves. These investigations make two soft soil layers emerge as a causative factor. The estimated 3D soil profile shows that the deformed ground overlaps the area where the weak soil layers are below the groundwater level. The 3D soil profile also suggests that groundwater lowering using existing wells can reduce the water-saturated area by 81%. Carbon dating shows that the causative layer formed before the Paleo-Kathmandu Lake dried up.