New pressure tunnel for the Kaprun main stage storage power plant

On 18 February 2025, with the traditional miner's greeting ‘Glück Auf’, the tunnel boring machine started its 5.6-kilometre journey from the Limberg valve chamber to the surge tank deep below the Maiskogel.

The ‘turning ceremony’ is an important moment for the VERBUND project ‘Kaprun 2029’. Some 200 guests were present when VERBUND's hydropower management, Michael Amerer and Karl Heinz Gruber, together with tunnel patron Kathrin Aberger-Dick and the ARGE representatives Jürgen Raschendorfer (COO Porr AG) and Bernd Raderbauer (Marti Tunnel AG), pressed the button to start the drill head turning. By the end of 2027, a new headrace will be built as part of the modernisation of the VERBUND Kaprun-Hauptstufe power plant. This will ensure that water continues to flow safely and efficiently from the Wasserfallboden reservoir to the power plant in the valley floor for decades to come.

The use of a tunnel boring machine is a proven method for excavating headwater channels. The machine used in Kaprun has already been successfully used in the Limberg II and Limberg III projects, with essential components and the cutting head being replaced and adapted for the current project. The dimensions are gigantic. The 100-tonne cutterhead, which has a diameter of 6.90 metres, is equipped with 42 cutting rollers, each of which has a diameter of 43 cm and weighs 130 kg. The entire tunnel boring machine has a length of around 190 metres and weighs 1,200 tonnes. The individual components were transported to the assembly cavern in 90 challenging journeys and assembled on site in around eight weeks.

VERBUND Hydro Power Managing Director Michael Amerer: "We are continuing on the path taken by the heroes of Kaprun after the Second World War for the reconstruction of Austria. Today, we have driven the first metres of the new pressure tunnel – an important moment for VERBUND. This pressure tunnel is the centrepiece of our project, which will upgrade the entire power plant to the latest state of the art by 2029, so that we can continue to supply all of Austria with green electricity and efficient flexibility from hydropower in the future.’

VERBUND project manager Maria Leo: ‘A launch celebration is always something very special. We are pleased that the preparatory work has gone so well and that it is now starting. The geological conditions for the advance are well known and the tunnel boring machine and the team are already familiar with our mountains from previous projects. Almost all of the work will be carried out underground. This means that the impact of the construction work is reduced to a minimum.’

Tunnel patron Kathrin Aberger-Dick: ‘I have close ties with the mountains in Kaprun and grew up with the high-altitude reservoirs. It is therefore a special honour for me to accompany the construction phase as the earthly representative of Saint Barbara, the patron saint of tunnel builders and miners. I hope that the underground work remains free of accidents and that the tunnel boring machine reaches its destination as smoothly as possible.’
Over the next few months, the tunnel boring machine will cut through the rock at an average rate of about 15 metres per day until it reaches its destination at the new surge tank in about a year. The new pressure tunnel is around 5,600 metres long, with an average incline of 0.50% and an excavation diameter of 6.90 metres.
The tunnel boring machine is supplied by rail. To do this, rails are installed in the tunnel. A particular challenge is the removal of the approximately 200,000 m3 of excavated material. The cutters break the rock into small chips, which are transported behind the cutter head by scrapers. From there, they are transported out of the tunnel on conveyor belts to a transfer station at the Limberg valve chamber and onwards via the existing tunnel system to a disposal site in the valley. This helps to relieve traffic in the region and minimise the impact of the construction work.

VERBUND is investing around 370 million euros in the ‘Kaprun 2029’ project.


Image credit: (C) VERBUND/Johannes Wiedl