(Proceedings of the Workshop on Rock Mechanics and Tunnelling Techniques, 10–12 October 2007, Gagtok (Sikkim) Organised by CBIP and ISRM (India))
Parbati Hydroelectric Project Stage – II lies in lesser Himalayan zone. Wide geological diversity and structural complexity characterize the area. The 800 MW Parbati H.E. project is ‘inter-basin transfer’ type, wherein the water of Parbati river is being diverted to Sainj river. A 31.5 km long HRT having 5 intermediate adits having 11 construction faces is in progress. Out of 31.5 km the longest portion of 13.1 km of HRT is being bored from two faces i.e. face-3 from upstream side with length 4.05 km is being bored using conventional DBM method where as the face-4 having 9.05 km length is being excavated by mechanized hard rock TBM (Atlas Copco Jarva MK27) from downstream side. The terrain is this stretch of HRT between RD 10413 and 19463 m is lying in very rugged topography with geological complexities. Out of 11 Faces this faces have gone through several criticalities since the starting of excavation of HRT. In this paper we will discuss about the challenges faced and the adequate methods adopted to successfully overcome the difficulties. Since the encountering of Manikaran Quartzite during 28 March, 2006 the TBM advancement along the proposed alignment had been stalled intermittently for various reasons. Although penetration rate is not the only deciding factor, few other applied parameters like Torque, Thrust, Cutterhead rotation speed etc. are also important in estimating the rock mass quality. Some times even the disturbance in maintaining the tunnel geometry due to over breaks also brings the advancement rate down. Although the penetration rate in the rock may be good but due to the hindrance factors the advancement rates slows down.
Tunnel boring machine, Mechanized hard rock TBM, Topography, Alignment
