The design of unlined hydropower tunnels and shafts: 100 years of Norwegian experience

The main criteria for the successful design of the unlined pressure tunnels described here are based on 100 years of experience and development of more than 80 unlined pressure waterways in Norway, with maximum heads of up to 1000 m. International experience of collapses in special, challenging ground conditions from other countries are also included. Recommendations that have emerged from this review are to locate tunnels in suitable rocks with sufficient confinement to avoid hydro-jacking, which could lead to water leakage failures, and, to detect and provide sufficient support to local sections with unstable rockmass conditions, including swelling and/or friable materials.