Construction aspects of 1000 mW karcham-wangtoo hydroelectric project

This paper brings out the special construction aspects of various civil structures of 1000 MW Karcham-Wangtoo Hydroelectric Project located in South-West Himalayas. For construction of 88 m high concrete gravity dam at Karcham, which consists of 53 m deep foundation, jet-grouted cut-off curtain was made through upstream and downstream coffer dams to control the seepage into the dam pit. Articulated Volvo Dumpers were specifically procured for hauling out the excavated muck on the wet and steep haul roads from the dam pit. For construction of four 18 m wide 494 m long and 33 m high desilting chambers, the top arch was made by first excavating the central gullet which was widened from both sides, reinforced concrete lined and then the Chamber was excavated from top down with concurrent reinforced concrete lining provided on the walls. The 17 km long HRT has been excavated by conventional drill and blast method in heading (7.5 m) and benching (3.78 m) sequence. The Norwegian Method of Tunnelling (NMT) by using Barton's ‘Q’ system was adopted for rock classification and providing the rock support system. The tunnel encountered adverse geological features in 200 m length in extremely poor and flowing conditions wherein face advancement was done by following the ‘DRESS’ technique. The HRT also passed through very high temperature zone of upto 98°C in 350 m length wherein the heading excavation was done by multiple drift method and jetting of cold water in drill holes and surrounding areas to bring down the surface temperature below 80°C. At the Surge Shaft wherein due to poor geological conditions, the pilot shaft had to be partly sunk from top and the approach road to Surge Shaft top was yet to be available, a ropeway was erected for transportation of heavy equipment so as to start excavation from top. In machine hall cavern, the crane beam has been supported on the rock ledge. The Project adopted accelerated approach to execute the works well within the schedule.