Nonlinear response and damage evolution mechanisms of subsea tunnels in fault zones under static-dynamic loading

Abstract

Abstract To address dynamic hazards in unlined subsea tunnels within fault fracture zones under high static loads and intense blasting impacts, this study investigates their nonlinear response and damage evolution. Taking the Qingdao Jiaozhou Bay Tunnel as a case study, we employed a self-developed shock simulation system for 1:60 scaled physical model tests and numerical simulations. Multi-level impact loads (0.2–0.8 MPa) were applied under a 0.1 MPa hydrostatic confining pressure. Results reveal that wave impedance mismatch in fault zones causes energy trapping and stress concentration, while stress wave phase inversion at the free surface induces shallow tensile failure. Damage evolution exhibits four stages: microcrack initiation, thin-layer spalling, fault-zone block detachment, and full-ring crushing, with 0.6 MPa identified as the critical threshold for global instability. Numerical simulations confirm severe stress concentrations and incompatible deformations at the arch waist and fault contacts, with damage propagating deeply along fault interfaces. Consequently, targeted reinforcement of the arch crown and fault “wedge zone”, primary support toughening, and restricting peak blasting stress below 0.6 MPa (actual stress of 36 MPa in the engineering prototype) are recommended. This provides a robust theoretical foundation for blast-resistant subsea tunnel design.