Abstract: Flexible joint is a key factor in the seismic design of the immersed tunnel when crossing through variable strata. This paper presents a theoretical model of the seismic response of flexible joint of immersed tunnel through different strata. The analytical model consists of two flexible joints and three tube elements. The Pasternak two-parameter foundation model was used to simulate the subsoil, while the Euler-Bernoulli beam model was used to simulate the immersed tunnel. The force and deformation transmission conditions of the joint in the immersed tunnel crossing through variable strata were considered. The analysis was based on the type of immersed tunnel that connects the artificial island at both ends, and free end boundary conditions were used to simulate the connection at both ends of the tunnel. By applying the matrix transfer principle, an analytical solution was to assess the seismic response of joints in immersed tunnels, accounting for the traveling wave effect. Verification of the analysis scheme was performed using finite element simulation results, demonstrating that flexible joints can effectively reduce shear forces and bending moments at strata interfaces. Under free end boundary conditions, joint shear stiffness mainly affects the joint shear force, and joint bending stiffness mainly affects the joint bending moment. The phase angles of seismic waves differ when forces reach the maximum values. When seismic waves are vertically incident, joint experiences the minimal force.

Key words: immersed tunnel, flexible joint, seismic response, different strata, traveling wave effect