TIWAG-Tiroler Wasserkraft AG has completed the breakthrough of a 25.6km diversion tunnel in Austria’s Stubai Valley, marking a major milestone in the Kühtai 2 hydropower project and the wider Sellrain-Silz power plant group expansion.
The tunnel boring machine (TBM) reached its final point after four years of excavation, having begun operations on April 6, 2022, in Kühtai. The completed tunnel will serve as a pipeline connection to a new reservoir in Kühtai.
“This makes this tunnel one of the longest single-sided tunnels in the world,” said TIWAG Managing Director Alexander Speckle.
During construction, the TBM achieved a maximum advance rate of 63m per day, with more than 1km completed in its most productive month. The final breakthrough occurred at the Wilden Grube near the Daunkogelfernerbach water intake.
“The machine will be dismantled and transported away by a dedicated team of specialists in the coming weeks,” reported project manager Klaus Feistmantl.
The electrically powered TBM measured 334m in length and weighed over 800 tonnes. A total of 18,818 precast invert segments were produced and installed on-site in Kühtai to form the tunnel base.
“This type of tunnelling was certainly unique, and TIWAG has once again set new standards in construction,” emphasized Managing Director Speckle. “Special thanks go to the contractors and their employees.”
Work on the wider Kühtai project continues, with the 113m-high dam approaching completion. Around 6.9 million cubic metres of material excavated from the reservoir and underground works have been reused in dam construction. The structure has a base width of approximately 500m and a total volume of 6.9 million cubic metres.
A dam “crowning” ceremony is scheduled for July, with Governor Anton Mattle expected to attend.
Reservoir filling is planned to begin over the summer, supported by natural inflows and a new diversion channel designed to transport water to Kühtai along a gentle gradient.
The new power plant is scheduled to enter operation in 2027. A public open day at the construction site is planned for September 5, 2026.
The TBM used for the project, named ALESJA, was an acronym derived from the first names of employees involved in the construction: Aida, Lisi, Elisa, Sabine, Jacky and Anna.
