Nant de Drance – Underground pumped-storage powerhouse

Nant de Drance – Underground pumped-storage powerhouse

Client / Owner

Nant de Drance SA (Alpiq 39% - CFF 36% - IWB 15% - FMV 10%)


2008 - 2018

Total costs

1'818 million EUR

Project description

Construction of a new underground pumped storage power scheme between the existing Emosson and Vieux Emosson reservoirs (Switzerland).
The project involves heightening the Vieux Emosson dam by 20 m and constructing an entirely underground plant (overburden 600 m), including 14 km of access galleries, 2 head and tail race tunnels and pressure shafts, and 2 main caverns (main hall and transformer caverns).
The underground scheme is mostly built within the crystalline base of the Aiguilles Rouges Massif, in generally good to very good geological conditions.
The plant will be equipped with 6 no. 150 MW reversible Francis pump turbines. It is expected to produce 2'500 GWh per year and commissioning is to take place progressively between 2018 and 2019.


• Tender documents for the powerhouse caverns (900 MW project)
• Bid analysis for the extension to 900 MW
• Participation in site supervision & coordination team

Excavation and support system
• Verification of the preliminary design of the support for the caverns
• Assistance for additional geological investigation and rock mechanics in situ and laboratory testing
• Detailed design of support and lining of the caverns (calculations and construction drawings)
• As-built drawings

Reinforced Concrete

• Preliminary design of the bearing structures in the caverns
• Design of second stage concrete around pumps & turbines (with dynamic and thermal calculations)
• Detailed design of cavern structures (calculations and construction drawings)
• As-built drawings

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