Seismic structure-water-sediment-rock interaction model and its application to immersed tunnel analysis under obliquely incident earthquake

In this study, a transient seismic structure-water-sediment-rock (SWSR) interaction model is proposed to evaluate seismic response of marine structure in ocean space under obliquely incident earthquake, in which the dynamic interaction between structure and its surrounding media, and wave radiation effect of truncated semi-infinite far field domain are fully considered. One particular advantage of the model is that the sediment layer in ocean space is more realistically modelled as fluid-saturated poroelastic medium. Three main procedures are included in establishing the model: first, a finite element equation of near field domain is established to model multi-media interaction; then a viscous-spring absorbing boundary condition is used to simulate wave radiation effect of truncated far field domain; and in the last, equivalent earthquake loading is obtained from seismic free field response. The model can be solved by a standard time integration algorithm such as implicit Newmark’s method. The validity of the numerical framework to establish the SWSR interaction model is demonstrated by analyzing three degenerated models and comparing with reference solutions. The seismic SWSR interaction model is finally applied to assess seismic response of an immersed tunnel, with emphasis on the effects of sediment properties here including thickness, porosity and permeability, and the seismic wave incident angle on structural dynamic responses.