Long-term structural response of three-layer tunnel linings in fault fracture zones

Fault fracture zones can markedly affect deep water-conveyance tunnels, but their influence on long-term behaviour of three-layer composite linings remains unclear. A three-dimensional finite-element model of the LG6 section of the Pearl River Delta Water Resources Allocation Project was developed, and its structural modelling strategy was evaluated against in situ loading-test and operational-monitoring data. Faulted and fault-free conditions were compared, and 60-year behaviour was assessed by updating key material properties. Under an internal pressure of 1.3 MPa, the fault increased the maximum radial deformation of the steel tube and self-compacting concrete (SCC) from 0.85 mm and 0.84 mm to 0.93 mm and 0.92 mm, respectively, caused a peak SCC circumferential strain of 263 με near the B1–L1 joint and produced a more uneven bolt-stress distribution. Long-term degradation increased maximum radial deformation by 12.4–13.1% and progressively transferred load from the steel tube and SCC to the segmental lining. These findings demonstrate that geo-interfaces, including the faulted ground–lining contact and the multi-layer interlayer interfaces, play a governing role in mediating long-term load redistribution and deformation localisation. The proposed framework provides a basis for geo-interface-aware service assessment of composite water-conveyance tunnels in fault-affected ground.