Stability of the foundation trench of the immersed tunnel subjected to combined wave and current loading

•An integrated FEM model of wave-seabed interaction is used to investigate the effects of wave-current action on the slope instability for the foundation trench of immersed tunnel.•The wave and current induced seepage pressure in the seabed is determined by Darcy's law and considered as external load.•The consolidation status of foundation trench after excavation is obtained and set as an initial condition.•The factor of stability (FOS) for the slope depends on the relative distance between the wave crest and slope.•The minimum of FOS corresponding to the most dangerous situation is regarded as the stability index for the slope in the whole process of dynamic wave-current loading. The determination of stability for the submarine artificial slope is important in the construction of offshore structures such as immersed tunnels and embedded pipelines. Aimed at this issue, a two-dimensional (2D) integrated model is proposed to investigate the slope stability of the foundation trench for the immersed tunnel under the combined wave and current loading, as in the real marine environment. The Reynolds-Averaged Navier-Stokes (RANS) equations are solved to simulate the wave field, meanwhile the current is realized by setting boundary inlet and outlet velocity at both sides. The interface between water and air is tracked by conservative Level Set Method (LSM). The wave-current induced pore pressure in seabed is calculated by Darcy's law, and the shear strength reduction method is adopted to judge the damage of the elastic-plastic seabed slope which is described through Mohr-Coulomb constitutive model. The wave-current model is validated through comparing with experimental data and analytical solution. The consolidation status of foundation trench after excavation is obtained and set as the initial condition for analysis. The factor of stability (FOS) for the slope is demonstrated to depend on the relative distance between wave crest and slope. The minimum of FOS corresponding to the most dangerous situation is regarded as the stability index for the slope with specific slope ratio in the whole process of dynamic wave-current loading. Through the parametric analysis based on this new evaluation method, the effects of soil strength parameters, slope ratio and current direction on the slope stability are discussed in detail.