Construction of two inclined headrace tunnels for a new pumped storage power plant in Switzerland has just been completed with breakthrough of the tunnel boring machine (TBM) on the final bore.
Main contractor Marti Tunnelbau used an Herrenknecht TBM to drive the 5.2m diameter, 1,030m long tunnels inclined at 40 degrees through limestone to connect the upper reservoir with the machine hall cavern on the Linthal project.
Linthal, which is near Limmern, will become Switzerland’s largest pump storage power plant when it is operational in 2015. The facility will use water from the Muttsee lake and pump water up 600m through the tunnels at times of low energy demand, ready to generate 1,000MW of power at peak times.
Marti used a Gripper TBM to carry out the tunnelling work and cut through the rock with strengths of up to 120MPa and complex faulting. To ensure the TBM could not slip backwards during the tunnel drive, Herrenknecht and Marti worked to develop a double anti-reverse lock with full back-up redundancy of the available bracing levels for the 130m long, 800t TBM.