Analytical solution for longitudinal seismic response of immersed tunnel connecting artificial islands crossing different strata

Abstract

Immersed tunnels typically pass through zones with different soil properties and may be subjected to earthquake threats. This paper presents a theoretical model using two flexible joints and three tube-elements for the longitudinal seismic response analysis of immersed tunnel connecting artificial islands. According to the reaction displacement method, the governing equations for bending of the immersed tunnel are established. Based on the matrix transfer principle, the end boundary conditions and the joint continuity conditions were considered in the analytical model. The analytical solutions were verified using finite element simulation results. Results indicate that the fixed and hinged end conditions have large shear forces on both ends, while the fixed end conditions have large bending moments. The free and roller end conditions have large vertical displacements on both ends, while the hinged end conditions have large rotation angles. The free end conditions can better reflect the boundary conditions of immersed tunnel connecting artificial islands. The flexible element joints can significantly reduce the shear forces at the interface of different strata, but also produce larger deformations at the joints. However, this amount of deformations can be accommodated by the flexible joints themselves, thus minimizing the damage to the immersed tunnel under seismic loading.