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All diameters, all grounds, all challenges

Nant de Drance pumped-storage power plant

Underway in all directions

For the benefit of nature: The underground infrastructure of the Nant de Drance pumped-storage power plant only has low impact on nature and the environment. Herrenknecht technology makes this possible. The closed circuit between the two reservoirs does not have any influence on natural water courses.

________________ The power plant technology for the Swiss pumped-storage power plant Nant de Drance is being installed underground. A Herrenknecht Gripper TBM drives the 5.6-kilometer-long access tunnel (5). Following successful pre­vious projects, the hard rock TBM was especially modified for this jobsite. The back-up system, which serves to supply the actual tunnelling unit, is adapted to the tunnel incline, for example. The tunnel boring machine has to deal with a gradient of up to 12 percent and curve radii of 500 meters. Disturbance zones are explored by systematic pre-drillings. In areas with very high water pressures, the rock to be bored through is stabilized with concrete in­jections. Two vertical pressure shafts, the penstocks (2), connect the Vieux Emosson reservoir (1) with the power house cavern (3) inside the Alps. The Herrenknecht Raise Boring Rig (RBR) drills vertically downwards, and in the next working step, the pilot borehole is reamed to a diameter of 2.44 meters. Subsequently the borehole is enlarged to 8.40 meters using a Shaft Drilling Jumbo.

The Herrenknecht Gripper TBM, which was especially adapted to the project, proved its worth, dealing with a gradient of 12 % and curve radii of 500 m.

For vertical pressure shafts, the Herrenknecht Raise Boring Rig produced a pilot hole with a diameter of 2.44 m in two working steps – with top daily performances of 62 m when pre-drilling and 33 m when reaming backwards. 

With a Herrenknecht Shaft Drilling Jumbo, the penstocks are being enlarged to a diameter of 8.40 m.

Tunnel lengths: 5,600m, 2× 424m

Geology: gneiss, graywacke, granite


TBM: Marti Tunnelbau AG

RBR: Marti Contractors Ltd.

Shaft Drilling Jumbo: Östu-Stettin Hoch- und Tiefbau GmbH

Gripper TBM, S-522
Diameter: 9,450mm
Cutterhead power: 3,500kW

Raise Boring Rig (RBR), MI-005
Installed power: 600kW
Diameter drilled: 2,440mm

Shaft Drilling Jumbo, MI-009
Configuration: 3 booms
Diameter drilled: 8,400mm

Navigation, monitoring

Nant de Drance, Switzerland

Project background

The Nant de Drance plant uses the difference in elevation between the Vieux Emosson (1) and Emosson (4) reservoirs. The closed circuit between the two reservoirs does not have any influence on natural water courses. Since the power house cavern (3) is underground, impact on the environment is low. The plant is designed to render 900 MW turbine and pump output. The power can be made available within 2 minutes. This is especially important for Swiss Railways (SBB): In the morning, when locomotives start almost simultaneously and according to timetable in all parts of the country, the power needed amounts to several 100 MW.

Herrenknecht technology for vertical shafts

Connection to the machine cavern: The Raise Boring Rig by Herrenknecht is sinking two pressure shafts. The drilling operations are remote controlled from a control cabin.
Safe pipe handling: In Raise Boring Rigs, the supply and removal of drilling rods at the borehole is carried out by a hydraulic gripper arm known as the pipe handler. This reduces physically strenuous work and provides for a high level of work safety.

Penstocks, the pressure tunnels for hydropower plants, run vertically or on a downward slope. The appropriate machine system to build such galleries can be chosen from the Herrenknecht range according to the project conditions. In Nant de Drance, two connecting shafts between two caverns located one above the other are being built. In this operation, the modularly designed Raise Boring Rig that can be quickly installed and easily removed is being used. The rig makes a vertical downward pilot drill with a diameter of around 300 millimeters down from the upper cavern. In the lower cavern, the drill bit is replaced with a reamer which enlarges the borehole as it is pulled back up. Then the shaft diameter is enlarged to 8.40 meters using a Shaft Drilling Jumbo. 

Flexible drilling: The Shaft Drilling Jumbo is able to produce shafts with a diameter of up to 12 m with varying drill patterns.
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