Research on the prestress Regulation of double-layer lining of shield water tunnel under high internal water pressure

Prestressed double-layer lining (segmental lining and prestressed lining) of shield tunnels has good seepage resistance and strong stability, and is a new type of support structure with great potential in high internal water pressure water transmission projects. For prestressed water conveyance tunnel projects, the reasonable value of lining tensioning prestress is the key to the economy and safety of the project. Accordingly, relying on the Pearl River Delta Water Resources Allocation Project, designed similar model tests for prestressed double-layer lining of water conveyance shield tunnels under the completed cable tension condition (CCTC) and design water pressure condition (DWPC) and established the corresponding ABAQUS three-dimensional finite element model to investigate the variations in the mechanical characteristics of the double-layer lining structure under different prestress conditions. The study determined the reasonable prestress range for the inner lining under a design internal water pressure of 1.5 MPa. The results indicated that under the CCTC, the prestressed lining is pressurized in the whole ring, the overall displacement level of the segmental lining is lower than that of the prestressed lining, the double-layer lining contact surface has a tendency to be detached, and with the increase of the structural prestress, the pressurized damage of the prestressed lining concrete develops gradually. Under the DWPC, the double-layer lining contact surface is completely closed under the action of internal water pressure, and the cracking risk of prestressed lining concrete increases with the decrease of prestress. Through numerical simulation, the reasonable range of prestressing force for shield tunnel lining is 68 %σ_con ∼ 137 %σ_con, and the results can provide a reference for the design and construction of prestressed double-layer lining structures of similar shield water tunnels.