The design of remedial works to the Dharan-Dhankuta Road, East Nepal

Abstract

Purpose of mapping Parts of the Dharan-Dhankuta Road in East Nepal were seriously damaged by the Nepal earthquake of 21 August 1988 and subsequently by a locally intense monsoon storm on 12 September 1988. Detailed field mapping was carried out at several of the worst-affected hill sections of the road. The purpose of the mapping was to establish the nature and local extent of earthquake, and subsequent landslide, rockfall and erosion damage as a prerequisite for the design of road remedial works. A full account of the work is given by Roughton & Partners (1988). This is an example of post-construction stage land surface evaluation using the five-stage classification of mountain road projects proposed by Fookes et al (1985). The site The Dharan-Dhankuta Road is a 50 km long mountain road traversing the first two ranges of the Low Himalaya of East Nepal (Fig. 1). It was built between 1977 and 1982 under the UK Government’s overseas aid programme to the Kingdom of Nepal (Cross 1982). The epicentre of the earthquake on 21 August 1988 was in the Udayapur District, about 65 km to the west of Dharan (Fig. 1). The focal depth was c. 60 km and the surface wave magnitude (Ms) was 6.6 (Dikshit 1991). Three weeks after the earthquake, heavy rain fell over part of the site during monsoon thunderstorms. The 24 hour rainfall recorded in Dharan was c. 160 mm, most of which fell within a few hours.