The existing research shows that the immersed tunnel is significantly affected by the earthquake, but the damage will cause serious casualties and property damage, and it is difficult to repair. However, the shaking table test of immersed tunnel including seabed and seawater site is difficult to realize at present, and numerical simulation is generally used for analysis. It has been found that seawater layer, seabed site conditions and soil-structure interaction have a large effect on the seismic response of immersed tunnels, but most of the existing studies have used two-dimensional models to analyze. In order to determine the influence of three-dimensional seabed site on the seismic response of immersed tunnel. Firstly, a three-dimensional layered site wave analysis program was established by using the coordinate system transformation and transfer matrix method, and combined with the finite element dynamic analysis software, a three-dimensional seismic wave analysis method of seawater and seabed immersed tunnel coupling was proposed. Besides, the correctness of the method is verified, and the influence of multi-dimensional site characteristics on seismic response of seabed site is analyzed. Finally, the immersed tunnel of Hong Kong-Zhuhai-Macao Bridge in China is taken as an engineering example, and the effects of tunnel longitudinal slope, incidence angle of ground motion, thickness of soft soil layer and water depth on seismic response analysis are studied. The results show that there is a great difference between twodimensional and three-dimensional seabed site model in seismic response. When considering the soft soil layer, the vertical seismic response of three-dimensional seabed site is significantly greater than that of twodimensional seabed site.Moreover, the silty soft soil layer also has a significant effect on the seismic response of the immersed tunnel, there is an obvious amplification effect on the tunnel horizontal seismic response. Besides, the horizontal seismic response of tunnel will be amplified with the increase of tunnel longitudinal slope and incidence angle, while the seismic response of tunnel will be inhibited with the increase of seawater depth.

Sea-crossing bridges face complex site environments compared to onshore bridges, with the marine environment significantly influencing seismic responses. Despite this, current seismic design for these bridges relies on onshore earthquake records. Therefore, investigating the impact of seawater layers and site conditions on seacrossing bridge seismic performance is crucial. This paper investigates the influence of characteristics of offshore ground motion, site conditions, and hydrodynamic effect on the seismic performance of piers. Initially, based on the validated finite element model, 5 offshore and onshore strong ground motion records from K-NET were selected for assessing the seismic performance of piers. Subsequently, the effects of the water depth and site conditions on the seismic responses of piers were investigated. Finally, the effects of the size, shape, and boundary conditions on the piers were investigated. The result shows that the seismic response of piers under offshore ground motion exceeds that under onshore ground motion. In addition, the seismic response of the pier increases with greater water depth, while they exhibit a slight decrease with increasing soil depth. Notably, the larger the size, result in higher the hydrodynamic pressure, and square piers experience greater hydrodynamic pressure compared to circular piers.