Embedment of steel spiral cases in concrete: China's experience

A spiral case refers to a water passage in a substructure of a hydropower house. The substructure is thus also known as a spiral case structure (SCS). For medium and high head hydroelectric power plants (HPPs), inner walls of spiral cases are steel-lined. For a steel-lined SCS, the embedment condition of the steel liner (steel spiral case) in the concrete is the dominant factor to determine the composite system's structural performance. Hence the issue of embedment of steel spiral cases has been a controversial and much disputed subject concerning the design and construction of HPPs. The purpose of the current work was to share China's experience on methods of embedment of steel spiral cases in concrete. The work has highlighted China's design philosophy of P-type and M-type SCSs. It is a joint-IWP-resisting philosophy for balancing the structural strength against integrity of SCSs. The work has also underlined an innovative solution (NM-hybrid-type SCSs) for excessively uneven lifts of generator pedestal structures confronting N-type SCSs. We believe that the experience can broaden the world's current knowledge of the design and construction of HPPs.