By Lynda Myer
Following digging 431m in January, Hindustan Construction Co is making good progress on India’s Vishnugad-Pipalkoti Hydropower project.
In order to excavating the 13km tunnel, a 9.86m diameter Terratec hard rock double shield TBM is used by the project’s primary contractor, whereas its commissioning date was November last year.
As the largest double shield machine in the Indian Himalayan region, this TBM has been specifically designed for the construction of a crucial low-pressure head race tunnel.
While the cutterhead features 19in disc cutters and 12 large bucket openings, due to existence of its 4,200kW electric main drive delivering a torque exceeding 22,000kNm, excavation through hard rock is possible. As the TBM advances, universal reinforced concrete lining rings, 1,500mm wide and 350mm thick, are installed, each comprising five segments plus a key.
Construction of dams, waterway tunnels, vertical shafts, as well as a powerhouse with a generating capacity of 444 MW, are the contents of this hydropower project, which is almost located at 500km north-east of Delhi in the state of Uttarakhand.
Considering that by construction of a 65m-high diversion dam across the Alaknanda River, power generation facilitated by a gross head of 237m, this is a part of the run-of-river scheme and the reservoir will have a gross capacity of 3.63 million m3, of which 2.47 million m3 will provide live storage. The water conductor system will consist of a diversion/spill tunnel, three intake tunnels, three underground sedimentation chambers, a headrace tunnel, a surge shaft, two pressure shafts, and four penstocks, along with two separate underground caverns for turbine and transformer installations
Dolomitic limestone (33%), slates (64%) and the remaining 3% passing through critical geological sections, is the geological condition of the alignment for the Vishnugad-Pipalkoti Hydropower project. These sections include thrust zones, shear zones, and fault zones, which pose significant challenges.
Terratec has also provided the 13km-long continuously advancing tunnel conveyor for the project. It operates at a rate of 1200t/hour. Terratec says its patented Advancing Tail Piece levels the conveyor using an active hydraulic system to match the steering/rolling position of the TBM. This enables the smooth negotiation of any horizontal and vertical curves.
