Effects of As-built Interface Deviations on the Mechanical Behavior of Prestressed Concrete Inner Linings in High-pressure Water Conveyance Shield Tunnels: A Refined Three-dimensional Finite Element Study

High-pressure water conveyance shield tunnels may develop segment misalignment and geometric deviations at the interface between segmental linings and prestressed concrete inner linings. This study examined these effects in Contract B2 of the Pearl River Delta Water Resources Allocation Project. Field measurements informed a refined three-dimensional finite element model incorporating the surrounding rock, segmental lining and prestressed concrete inner lining. Circumferential stress responses were evaluated at representative circumferential locations and longitudinal sections during construction and water conveyance operation, including an operating internal water pressure of 1.3 MPa. The results indicated that, without misalignment, the inner lining remained in circumferential compression during both loading stages, although the end sections retained smaller compressive stress reserves than the middle section. Segment misalignment redistributed prestress and generated localised circumferential tensile stress concentrations, particularly near the crown and springlines at the tunnel ends. Tensile stresses could develop under some misalignment conditions described as satisfying assembly acceptance criteria. Ovality-related reductions in effective lining thickness also changed circumferential stresses, with a more pronounced response in the outer layer. Numerical design checks incorporating a prestressing-strand bending-moment amplification factor of 1.9 and a conventional-reinforcement safety-factor correction factor of 1.1 indicated improved cracking resistance under the assessed unfavourable conditions. These findings support supplementary structural checks of sensitive inner-lining regions rather than reliance on segment assembly tolerances alone.