Alliance Hydropower Plant Inn (Lot Maria Stein)

Completing a challenging hydropower tunnel system under demanding geological conditions

The Maria Stein lot formed part of the Alliance Hydropower Plant Inn hydropower scheme and marked STRABAG's first joint project with VERBUND in the Austrian hydropower sector. Following the termination of the original contractor, the continuation and completion of the works were entrusted to a consortium led by STRABAG.

The contract included the adaptation of the existing construction facilities, the recommissioning of two double-shield tunnel boring machines (TBMs), and the completion of approximately 22 kilometres of tunnelling works for the new hydropower plant at Prutz. At the time of takeover, only around 3 kilometres of the tunnel system had been excavated, while both TBMs were immobilised in geological fault zones and required complex recovery measures before tunnelling operations could resume.

Additional challenges arose from demanding ground conditions, including the encounter of asbestos-bearing rock in one tunnel section, requiring the implementation of comprehensive safety and protection measures throughout the excavation works.

Scope of Work

• Continuation and completion of tunnelling works after contractor replacement 
• Adaptation of existing construction facilities and infrastructure 
• Recommissioning of two double-shield TBMs trapped in geological fault zones 
• Completion of approximately 22 km of hydropower tunnels 
• Excavation works under challenging geological conditions, including asbestos-bearing rock 
• Construction of the dismantling cavern at Ovella 
• Grouting works along the entire headrace tunnel system 
• Closure and restoration of temporary construction access routes