Seismic behaviors of a floating submerged tunnel with a rectangular cross-section

A submerged floating tunnel (SFT) is an underwater infrastructure through which ground transportation can pass. Given that an SFT can be manufactured on land and assembled on water without long-distance underwater excavation, it can significantly reduce the construction period and cost and may therefore be highly appropriate for long-distance transportation. In this study, the two-dimensional seismic behaviors of an SFT system are examined. The principal effects of seawater upon the seismic behaviors of an SFT system are investigated. The hydrodynamic pressure from the wave equation for a fluid is calculated with rigorous consideration of the compressibility of seawater, the absorption of pressure waves by a flexible seabed, and the radiation of energy into infinity. The hydrodynamic pressure is applied to the structure while also considering the fluid-structure interaction. The dynamic characteristics of an SFT system are revealed from an application example. It is observed from the application that the compressibility of fluid, the depth of seawater, the location of the tunnel structure in water, and energy absorption by a flexible seabed influence the seismic responses of an SFT system substantially. Therefore, these effects must be considered rigorously for accurate and economical seismic designs of SFT systems.