Unlined high pressure tunnels and air cushion surge chambers

More than 80 unlined pressure shafts and tunnels with maximum water heads varying between 150 and 1000 m are today in operation in Norway. The majority of these were constructed during the years 1960 - 90. The oldest ones have, however, been in ope-ration for 80 years. The development of the general layout for hydropower plants as well as the different design criteria for unlined pressure tunnels are described. Experience from the operation is discussed. Operational experience from ten unlined air cushion surge chambers have been examined with respect to air leakage. Internal air pressure varies from 19 to 78 bars and chamber volumes from 2.000 to 120.000 m3.