Hydropower plant Kühtai – Invert segment


The 25.5 km long diversion tunnel Kühtai - Fernau is to be driven with TBM. The trafficked invert, which also acts as an abutment to the lining, is provided by segments in three designs adapted to different conditions.

The diversion tunnel for the hydropower plant Kühtai is being constructed by the JV SKW Kühtai, including the contractors Swietelsky, Jägerbau and Bodner. The tunnel is to be constructed using a TBM, lined where necessary and fitted with an invert segment. Construction logistics dictate that the invert has a flat surface for vehicles, rather than a trench. Three types of invert segment are provided according to the requirements of the lining: the unreinforced standard type L and the steel fibre reinforced types S for use with lattice girders and P with an integrated pump sump. The steel fibre reinforcement is designed for a residual tensile strength fR3 = 4 MPa with ductile failure mode.


  • 2021/22: Design of invert segments, structural calculations for handling and operational load cases

Project Facts

  • Project

    Hydropower plant Kühtai – Invert segment

  • Client

    JV SKW Kühtai

  • Function

    Segment design

  • Technical Facts

    Plant technical data:
    Turbine power: 140 MW
    Diversion tunnel: Unpressurised watercourse tunnel with modular lining
    Invert segment L: Light segment
    Segment S: Heavy segment
    Segment P: Segment with integrated pump sump

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