Linthal 2015 project
With the Linthal 2015 project, Axpo AG expanded the Limmern power plant to include a new pumped storage plant with a capacity of 1000 MW. The existing Limmern reservoir serves as the lower reservoir. The Muttsee lake at 2500 m above sea level was extended with an approx. one kilometre long dam and acts as the upper basin. Four turbines are housed in a new cavern control centre. The difference in altitude of 630 m between the Muttsee and the cavern control centre is overcome with two pressure pipes with a length of about one kilometre and a diameter of 6 metres. Together with the already existing power plant, the capacity increased to a total of 1520 MW.
Preliminary exploration of Muttsee
As part of the preliminary exploration for the project to heighten the Muttsee dam, Solexperts was commissioned to carry out two test campaigns. First, permeability tests were performed in the debris cones of Lake Muttsee to investigate their behaviour during rapid changes in lake level. Hydraulic tests were carried out in 40 m deep boreholes to determine permeabilities at different depths.
Preliminary exploration of caverns
The second campaign included in-situ stress measurements with the hydraulic fracturing (HF) method, dilatometer tests and hydrogeological tests in the area of the new cavern centre. The aim of these tests was to determine the rock elasticity, the permeability, the hydraulic pressure heads and the existing stress state in the rock. The parameters determined helped in the dimensioning of the structures and in the planning of the construction work.