Seismic response characteristics of subsea shield tunnels considering seawater-stratum-structure coupling

The seismic dynamic response of subsea tunnels in complex hydrogeological environments is crucial for ensuring their safe operation. This study investigates the combined effects of soil-structure interaction (SSI), cover-to-diameter ratio (C/D), and hydrostatic-hydrodynamic pressures on tunnel lining responses, using the Shantou Bay Tunnel as a case study. The Davidenkov constitutive model is employed to characterize the nonlinear dynamic behavior of marine soils, while the coupled acoustic-structure method is integrated into the finite element model to capture the interaction between seawater, seabed, and structure. Results indicate that, under 0.2 g seismic excitation at a water depth of 50 m, the peak tunnel diameter deformation ratio with SSI is 23.74% greater than that without SSI. As the depth increases, the combined hydrostatic and hydrodynamic pressures amplify the deformation ratio by 6% to 42% compared to hydrostatic pressure alone, suggesting that neglecting hydrodynamic effects at significant depths would substantially underestimate structural deformation. Furthermore, when the tunnel C/D is 1.5, the additional impact of hydrodynamic pressure is only 9% to 14%, which is considerably lower than the 22% to 66% observed for a C/D of 0.9. Additionally, the hydrodynamic pressure on the seabed exhibits a non-uniform “double-peak and single-trough” distribution due to the presence of the tunnel.