Fully Coupled Numerical Analysis of Seismic Behavior of a Shield Tunnel Embedded in Nonuniform Liquefiable Soils

Large‐diameter subsea shield tunnels in coastal areas may inevitably cross saturated soils with different liquefaction resistance and are thus susceptible to seismic damage during earthquakes. This study investigated the seismic response and deformation mechanism of a shield tunnel embedded in nonuniform liquefiable soils subjected to transverse ground shaking based on fully fluid–solid coupled analyses. The UBC3D‐PLM and HSSMALL constitutive models in PLAXIS 2D respectively used to capture the nonlinear behaviors of liquefiable and nonliquefiable soils under cyclic loading. An elastic–plastic design method was proposed to simulate the mechanical behavior of segment joints. The obtained results demonstrate that under transverse seismic loading, the tunnel in the nonuniform liquefiable soils is primarily subjected to compressive forces rather than shear forces during earthquakes, and the deformation mode of the tunnel is crown heaving rather than the overall uplift of tunnels in uniform liquefiable soils. Under rare seismic events, the tunnel’s bending moment, overall tunnel deformation, and opening of longitudinal joints exceed the elastic limits, posing a risk of plastic damage. Therefore, it is necessary to implement corresponding mitigation measures to enhance the seismic performance of tunnels in nonuniform liquefiable soils.