TBM makes good progress on Vishnugad-Pipalkoti Hydropower project

The project’s primary contractor is using a 9.86m diameter Terratec hard rock double shield TBM to excavate the 13km tunnel. It was launched in November last year.

The TBM – the largest double shield machine in the Indian Himalayan region – has been specifically designed for the construction of a crucial low-pressure head race tunnel.

The cutterhead features 19in disc cutters and 12 large bucket openings. Its 4,200kW electric main drive delivering a torque exceeding 22,000kNm will allow excavation through hard rock. As the TBM advances, universal reinforced concrete lining rings, 1,500mm wide and 350mm thick, are installed, each comprising five segments plus a key.

The hydropower project, approximately 500km north-east of Delhi in the state of Uttarakhand, includes the construction of dams, waterway tunnels, vertical shafts, and a powerhouse with a generating capacity of 444 MW.

The run-of-river scheme involves the construction of a 65m-high diversion dam across the Alaknanda River, with power generation facilitated by a gross head of 237m. 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

The alignment for the Vishnugad-Pipalkoti Hydropower project crosses primarily Dolomitic limestone (33%) and slates (64%), with the remaining 3% passing through critical geological sections. 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.