Planning, Design & Construction of Diversion Tunnel for Arun-3 HEP (900 MW) in Nepal - A Case Study Garg Kuldip1, Kapoor Jaswant1, Kapoor Jaswant2, Abrol R.K.3, Bansal S.P.4 1Manager (Civil Design) SJVN Limited, Corporate Office, Shimla (H.P.), India 2AGM (Civil Design) SJVN Limited, Corporate Office, Shimla (H.P.), India 3CGM (Civil Design), SJVN Limited, Corporate Office, Shimla (H.P.), India 4Director (Civil), SJVN Limited, Corporate Office, Shimla (H.P.), India Online Published on 28 September, 2023. Abstract Arun-3 HEP is a Run of the River (RoR) type hydropower project presently under construction on River Arun in Sankhuwasabha district of Nepal. The Project comprises of a 80m high concrete gravity dam, Power Intake on left bank, 11.77 Km long & 9.5m dia Horse Shoe shaped Head Race Tunnel, 149m deep Surge Shaft, Underground Power house & Tail Race Tunnel/Outfall structure. The project is currently under advanced stage of construction. For undertaking construction works for concrete gravity dam, 11m dia & 429m long horse shoe shaped diversion tunnel has been excavated through weak/fragile rock mass to divert 1300 Cumecs of diversion design flood. To enable the design diversion flood through Diversion tunnel, a 27m high u/s colcrete cofferdam and 5m high d/s earthen cofferdam have also been constructed. The Himalayas being young and fragile posed a geologically challenging environment for construction of the diversion tunnel. The u/s colcrete cofferdam has been designed as semi-permanent structure with Overtopping allowed. The Diversion tunnel is presently commissioned and is under operation. This paper presents the planning & design aspects for the river diversion arrangement as well as the modification adopted for the tackling the cavity/chimney formation inside during construction of the diversion tunnel. Top |