Tunnel breakthrough a key milestone in 140-MW hydropower project in Nepal

The breakthrough ceremony for the tunnel, which will carry water from the reservoir to the 2-turbine underground power station, was held at the Tanahu headworks. Tractebel was on site to mark the occasion, in the presence of representatives from the Nepal Electricity Authority, the Ministry of Energy, local authorities, contractors and other project personnel. The successful excavation — a significant milestone — brings the project to 50% completion.

Transparent cooperation of project stakeholders delivered a safe and sustainable underground structure: the contractor’s geotechnical designer and the contractor’s and Tractebel’s engineering geologists worked as one team.

Tractebel supports tendering, construction supervision and design checks

Our team from Tractebel in Germany, in association with Canadian-based Manitoba Hydro International, is carrying out the contract by client Tanahu Hydropower Limited for:

• Preparation of tender documents
• Tender evaluation
• Construction supervision
• Design checking
• Advisory services during project operation and maintenance

The first of the three construction packages (headworks; waterways, power plant, and hydromechanical works; and the 33-km transmission line) began in December 2018. The project is expected to be commissioned in 2026.

Real-time support optimization in difficult ground conditions (graphitic slate), under a high stress regime

Excavation and temporary support in dolomite, 50 metres before breakthrough

The Tanahu hydropower project, with its estimated generation of renewable energy of around 1.1 TWh, including 586 GWh during the first 10 years, will greatly benefit the Nepalese people and economy. Tanahu will further stabilize the national grid, and at the same time support the national by exporting energy to neighbouring countries such as India.

“Since the headrace tunnel is the only waterway between the reservoir and the underground powerhouse, resilience and serviceability are vital factors for the entire lifetime of the project,” says Renos CHRISTAKIS, Senior Engineering Geologist with Tractebel in Germany. “For the last 29 months, the contractor’s designer, its engineering geologists and hundreds of workers, with the support and technical input of Tractebel and in particular its geologists, worked together and managed to excavate a large-span underground structure through challenging rock mass conditions; conditions that required excellent cooperation, mutual understanding, real-time support optimization techniques, diligent monitoring and above all, engineering integrity.”

Renos CHRISTAKIS, Senior Engineering Geologist, Tractebel in Germany

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