Cyclic fatigue in unlined hydro tunnels caused by pressure transients

Regulated hydropower is currently the most capable load balancing technology for the future renewable energy system which will be characterized by a large share of unregulated energy from solar and wind power. Increased application of hydropower for balancing means that more frequent pressure transients will occur in the waterway system. In this article, the authors explain how such pressure transients cause pore pressure fluctuations in the rock mass surrounding the tunnel periphery and may lead to cyclic fatigue. An explanation of the mechanisms that contribute to fatigue is also presented along with the most significant factors that can accelerate the fatigue development. The possible applications and limitations of these findings are discussed and recommendations are given.