Hydropower plants are of great relevance for European energy production. Vertical shafts in comparison to inclined shafts may serve as a cost alternative in case of favourable ground conditions. Vertical shafts have a higher ground coverage compared to surface parallel inclined shafts. The increased rock mass cover and therefore higher in-situ stress magnitudes (e.g. decreasing risk for hydro-fracturing) may allow unlined solutions instead of cost intensive steel lining (providing that water losses are economically acceptable). Both, concrete lining and rock mass are subjected to transient loading conditions during operation. Depending on strength and thickness of the concrete lining, unreinforced concrete tends to crack more easily and intense upon exceeding a critical effective internal water pressure. The structural integrity is associated with the number of hydraulically induced cracks and the crack width at a given internal water pressure. The design of reinforcement depends on the bedding of the lining (e.g. deformability of the rock mass), the hydraulic conductivity of the rock mass in relation to the concrete lining, the external and internal water pressure, and the in-situ state of stress. The paper presents a procedure to determine the stress state within a concrete liner and the surrounding rock mass. Furthermore, the reliance and application of the European Standard (Eurocode EC 2) for the geotechnical and structural design of concrete lined pressure shafts is discussed.
Modern pump storage schemes allow immediate production of peak current upon demand. Due to the availability of modern shaft construction methods, vertical penstocks may serve as an alternative to common inclined shaft solutions with steel lining. Even though, economic considerations may favour the implementation of a concrete lining in order to minimize head losses and thus allow smaller excavation diameters and the abdication of a rock trap.
