Prediction of rock support in Melamchi Tunnel, Nepal

The Melamchi Diversion Scheme is a water supply project to a rapidly expanding Greater Kathmandu in Nepal. The proposed tunnel for the project is about 29 km long with a nominal diameter of 2.8 m and is to convey 8 m(3)/s flow of water from the Melamchi River to the Bagmati River. The major type of rock in the project area is gneissic rock. The geology and topography is favourable for a small diameter tunnel. The paper compares the prediction of rock support in the tunnel at different stages of the pre-construction phase. As the test adit revealed more information of the rock condition at the tunnel level, the quantity of support and cost predicted earlier became significantly higher.