Extension of the existing power station with a pumped storage scheme. Increase of the total power production from 450 to 1’450 MW and water storage volume from 9 to 25 Mio. m³. The work will be executed at various sites. The only possibility for access from the valley in Tierfehd to the work sites is by means of cable car.

The work involves the following stations:

•     Tierfehd 817 metres above sea level
•     Cavern Limmernsee, alt. 1’800 m
•     Ochsenstäfeli Limmernsee, alt. 1’800 m
•     Access tunnel, alt. 2’350 m
•     Muttsee, alt. 2’446 m

• 2 inclined pressure shafts, drilled with a  tunnel boring machine, l = 2 x 1’120 m, Ø = 5.2 m, inclination = 45°
  • Machine- and transformer caverns for 4 groups of 250 MW each
  • Access and service tunnels by drill and blast
  • Two tailrace galleries, l = 530 m, Ø = 5.5 m
  • Headrace gallery, l = 575 m, Ø = 8.0 m
  • Valve chamber
  • Concrete dam Muttsee, l = 1’050 m, h =35 m
  • Surge shaft h = 130 m, Ø = 11.7 m
  • Concrete work above ground for the power station intake and outlet structures at Limmernsee and at Muttsee
  • Crusher and concrete plant (April, 2011 = 250’000 m³)
  • Concrete aggregate processing plant
  • Management of spoil dump area at 2‘470 m altitude

• Complete underground hydroelectric power station - Access from the valley only by cable car - High alpine environment with big potential of natural hazards - Very limited space in all construction areas - Unstable weather conditions Board and lodging: - Tierfehd, equipped for 420 employees - Muttsee, equipped for 120 employees