Mitsubishi TBM Breaks Through Parbati Stage II Hydropower ShaftA Mitsubishi-Boretec-NFM refurbished TBM has achieved the breakthrough of the second inclined pressure shaft of the Parbati stage II hydroelectric scheme in Himachal Pradesh, India. Stage II of the Parbati hydroelectric lies in the lesser Himalayan zone and will supply a capacity of 800 MW. It is one of the major hydro projects under construction for India's National Hydroelectric Power Corporation (NHPC). Visit www.nhpcindia.com/hp/parbati2hp.htm The Parbati project is built in three stages. Stage II and Stage III are currently under construction. Stage III comprises a 6 m-diameter and 31.5 km-long concrete-lined headrace tunnel at Pulga in the Parbati valley up to a surge shaft in Sainj valley. The project also includes two 4.5 m intake tunnels, amongst the main underground works.The 17 m-diameter 130 m-deep vertical surge shaft carries water to two 3.5 m-diameter pressure shafts, which then bifurcate into four 2.5 m-diameter penstocks to feed turbines in the powerhouse.The two pressure shafts are 2,050 m and 2,120 m long respectively, whereof 1,545 metres of two shafts incline at 30° to the horizontal and contain a bored diameter of 4.88 m with a finished diameter of 3.5 m. The 4.88 m-diameter double-shield TBM has been used for excavating the inclined section of these pressure shafts. The second, right shaft successfully holed through in a record period of 136 days. Excavating the right inclined pressure shaft began on 17th July, 2006. The final breakthrough was achieved on 30th November. Mitsubishi designed the TBM specifically to work in an inclined tunnel. The double-shield TBM used for this job contained several prominent features. The main drive motors consist of six units of 250 kW each. The machine is equipped with 33 432 mm cutters. Maximum operating load per cutter is 267 kN. Normal operating power consumption has been estimated as 1,500 kVA at the project start. The TBM has gripper pads and is equipped with an anti skidding device. The machine is also equipped with a probe drilling machine and segment erector. Visit www.mhi.co.jp/kobe/mhikobe-e/products/kenki/index.htmlThe machine has been erected inside the inclined pressure shaft. This required to construct two 35 m-long chambers, 12 m-high at the end of an adit. After boring the first, left pressure shaft the TBM was dismantled at the top and taken out again to be assembled in the second pressure shaft at the bottom. Two dismantling chambers at the top were constructed. Hexagonal precast segments were installed for supporting the ground. The pressure shafts will be steel lined. The excavated muck was transported through a steel trough and flushed with a jet of water from the working face down to the adit bottom in a hopper where water and muck were separated. The dry muck was transported from the hopper out of the tunnel by conveyor belt. Click here to read more on the project and in/38. 04/07.