Comparative Analysis of Longitudinal Seismic Responses of Rigid, Flexible, and Semirigid Immersed Tunnels Using the Analytical Method

To adapt to complex underwater geological conditions, immersed tunnel projects have gone through the development from rigid and flexible to semirigid immersed tunnels. The stiffness of segment joints and the element joint could reflect the differences in structural characteristics of the three types of immersed tunnels. This paper presents a theoretical model using segment joints, the element joint, and 16 segments for the longitudinal seismic response analysis of the three types of immersed tunnels. Based on the matrix transfer principle, the end boundary conditions and the continuity conditions for the forces and deformations at the segment joints and element joint were considered. Analytical solutions were validated by verifying the established laws. Results indicate that the semirigid immersed tunnel, in contrast to the rigid immersed tunnel, can reduce shear forces and bending moments along the longitudinal direction by using segment joints and the element joint. In addition, compared with the flexible immersed tunnel, the semirigid immersed tunnel has higher overall stiffness and better continuity of deformation between the adjacent soil regions through the prestressed tendons inside the tube element. The semirigid immersed tunnel is a viable solution for complex geological conditions where the strata change every few tens of meters.