Strain measurements at the transition from a rock supported to an unsupported steel lined pressure tunnel at the Kaunertal hydropower station

A new steel‐lined pressure shaft was constructed for the existing Kaunertal high‐head hydropower plant in the years 2012 to 2015. Before starting operation, initial filling tests were carried out in particular to investigate the behaviour of a steel penstock at the transition from a steel lined pressure tunnel to an open pipe section. Cases with and without steel ring bearings (thrust rings) to transfer the end loads to the rock mass were numerically analysed and compared to measurements. A conclusion is drawn from the measurement results how to arrange and analyse such a steel pipe transition into the rock mass, which may for example occur at valve chambers.