A new steel-lined pressure shaft and surge tank are being constructed for the existing Kaunertal high-head hydropower plant. The inclined shaft with a diameter of 4.3 m is approx. 1430 m long and is designed for a pressure head of 100 bar. The steel lining is fully embedded and installed inside the precast concrete segmental lining, which was earlier erected as the tunnelling work progressed. Steel design criteria take into account that the internal pressure is shared between the pipe steel and the rock mass according to the stiffness ratio of lining and rock mass.
To support the development of steel lining design and material specifications prior to award of contract, the permissible steel strength vs. ductility was investigated together with the compatibility between pipe material and welding material and the brittle fracture behaviour. In particular, the high-performance steel and welding materials require a detailed fracture mechanics analysis to establish whether selected materials fit project requirements. Extensive tests were carried out on sample pipes - partly on a full-size model - by the bidders to select the steel and welding materials. An analysis of the tests revealed interesting results and dependencies on material strength, welding process, filler material and other parameters.
An overview of the project, which is being implemented between 2012 and 2015, the design criteria for the steel-lined shaft and the material specification are presented in this paper.