By rosebell
As a key component of the €370m Kaprun 2029 hydropower modernisation project in Austria, excavation of a 5.6km pressure tunnel has been started by Austrian electric utility Verbund.
Through ensuring a stable water supply from the Wasserfallboden reservoir to the facility in the valley, this tunnel is due to support long-term energy production at the Kaprun-Hauptstufe power plant.
Following that the tunnel boring machine started operations on 18 February 2025, this project reached a milestone.
Previously being used in the Limberg II and Limberg III projects, the tunnel boring machine has been modified for this phase of construction, whereas it is consists of a 100-tonne cutterhead with a diameter of 6.90m, fitted with 42 cutting rollers, each measuring 43cm and weighing 130kg.
With 1,200 tonnes weight, the entire system spans 190m and components were delivered in 90 separate shipments and assembled in an underground cavern over eight weeks.
According to 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.”
“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,” said Verbund project manager Maria Leo.
The estimated daily excavation advance for this machine is at a rate of 15m, reaching the new surge tank within a year.
As an incline of 0.50% and an excavation diameter of 6.9m has been considered for the completed tunnel, to facilitate the excavation process, a rail system is going to be installed inside the tunnel.
Approximately 200,000m³ of excavated material will be transported via conveyor belts from the cutterhead to a transfer station at the Limberg valve chamber before being moved through existing tunnel infrastructure to a designated disposal site.
The scheduled date for completion of the headrace tunnel is end of 2027.
