Slope mass rating in middle mountain of Nepal: a case study on landslide at Rabi VDC Opi Village, Kavre

Abstract

The study landslide area lies on Opi Village Development Committee (VDC) of Kavre district at the north west (about 3 km) of Dhulikhel Bazar and North east (about 4km) from Banepa Bazar of Nepal. The area is composed of rocks of Bhimphedi group of lesser Himalayan crystalline. The rock on this group comprises Precambrian green schists metamorphosed rocks of schist quartzite and few marble horizons. Geomorphologically, the failure site is located in between a stream gully on the toe and residual soil on the crown. Field observation, attitude measurements, sampling and lab analysis and GPS mapping are the main methods to find the dimension and characteristics of the landslide.

It is found that there are few major discontinuities that play the role for the rock/soil slides around the area. In the field measurement the orientation of the rock foliation around the area is 220°/35°. The major discontinuities are 205°/40° and 150°/60°. These joint sets play the main role to the plane as well as wedge failures around the area.

Slope Mass Rating (SMR) is calculated based on values of Rock Mass Rating (RMR), other joints and slope orientation. The calculated value of SMR is 34, which indicates the calculated value lies on IV class (Bad), unstable having planner or big wedges failure of SMR and needs to be corrective measures in the slope. The calculated result matches the site condition and characteristics of the Opi land slides.