Current experiences in the design and construction of pressure tunnels and shafts

Abstract

Hydrotechnical power waterways in the form of pressurized tunnels and shafts pose geotechnical requirements on the surrounding underground, which vary significantly from those of other infrastructure tunnels, like traffic or mining tunnels. The excavation process and the primary support design requirements of traffic and hydrotechnical tunnels are the same. Nevertheless, the structural design aspects of the final (inner) lining of these two tunnel types are different and misunderstanding of these differences is often the reason for problems occurring in operation. Although the technical issues related to the subject were correctly identified and solved decades ago, it appears that some of the basic technical aspects are not addressed correctly in the design and execution of some hydrotechnical tunnels today. This fact was the main motivation of the authors to summarize current experiences of design and construction in hydropower projects worldwide. The primary focus is placed on the technical requirements for the final hydraulic lining of tunnels and shafts. For unlined and shotcrete lined tunnels, the design is mostly performed by classification systems. The limitations and risks of this approach are explained. For concrete lined and steel lined tunnels and shafts, current experiences and preconditions for the state-of-the-art design approaches are discussed.