Terratec's Hard Rock Double Shield Tunnel Boring Machine (TBM) is achieving significant milestones on the Vishnugad-Pipalkoti Hydropower Project in India, the company has announced. The Ø9.86m TBM has successfully excavated 431m in January 2024, marking a substantial advancement for the project.
The Vishnugad-Pipalkoti hydropower project, located in the Uttarakhand state, is a key initiative encompassing the construction of dams, waterway tunnels, vertical shafts, and a powerhouse with a generating capacity of 444MW. The project's critical component is the construction of a low-pressure headrace tunnel, for which the Double Shield TBM has been specifically designed. This TBM, the largest of its kind in the Indian Himalayan Region, is tailored with custom features to efficiently complete the 13km tunnel, which is vital to the hydroelectric power system. The machine is presently working for Hindustan Construction Co. Ltd. of India, the primary contractor for this project.
The project involves the implementation of a run-of-river scheme, which includes the construction of a 65m-high diversion dam across the Alaknanda River. Power generation is facilitated by a gross head of 237m. The reservoir is designed to have a gross storage capacity of 3.63 million cubic meters, with 2.47 million cubic meters allocated for live storage. Additionally, the water conductor system comprises a diversion cum spill tunnel, intake tunnels, underground sedimentation chambers, a headrace tunnel, a surge shaft, pressure shafts, and penstocks. Furthermore, two separate underground caverns are being constructed to house turbine and transformer installations.
The alignment for the project primarily traverses 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 necessitating the TBM's specialized engineering.
Terratec is providing the Continuously Advancing Tunnel Conveyor for the project. Designed to meet the specific demands of the project, this will have a length of 13km and operate at a rate of 1200t/h. The conveyor is capable of efficiently handling the various materials extracted by the TBM along the entire length of the tunnel. The conveyed materials are expected to vary from sandy gravel to boulders.
The TBM's CutterHead boasts 19'' disc cutters and twelve large bucket openings, facilitating excavation through expected hard rock with its 4200kW electric main drive delivering a torque exceeding 22,000kNm. As the TBM advances, universal reinforced concrete lining rings, 1,500mm wide and 350mm thick, are installed, each comprising five segments plus a key.
