Preliminary Field Assessment of Sinkhole Damage in, Pokhara, Nepal

Abstract

Since November 2013, numerous sinkholes have been forming in the Armala area of Pokhara Valley, Central Nepal, posing serious threat to local residents. In order to provide measures aimed at reducing sinkhole risk, investigations into the cause and features of the sinkholes are crucial. This paper presents early research results based on two damage surveys conducted in June 2014 and November 2014 in the Armala area. Comparison of photos, taken in the two surveys, clearly indicates not only the formation of new sinkholes, but also the re-activation of filled sinkholes. By means of dynamic cone penetration tests and surface wave method investigations, qualitative characterization of the soil profile was attained, and shallow weak soil layers which are believed to be the location for future sinkholes could be identified. On the basis of the field investigation results, possible sinkhole formation mechanisms are identified for the Armala area. Furthermore, results of a reconnaissance survey conducted in the Armala area in early May 2015 (following the 2015 Gorkha Nepal Earthquake, which occurred on April 25th) are also reported. Although the epicentral distance to Pokhara was closer than Kathmandu, which suffered from severe damage, no major apparent effects of the earthquake were observed in the sinkhole damaged area.