Waves can cause significant accumulation of pore water pressure and liquefaction in seabed soils, leading to instability of foundations of marine hydrokinetic devices (MHKs). Geostatic shear stresses (existing around foundations, within slopes, etc.) can substantially alter the rate of pore pressure buildup, further complicating the liquefaction susceptibility assessments. In this study, the development of wave-induced residual pore water pressure and liquefaction within sandy seabed slopes supporting MHK structures is evaluated. Unlike most earlier studies that excluded the impact of shear stress ratios (SSR) on the residual pore pressure response of sloping seabeds, asymmetrical cyclic loadings are considered herein for a range of SSRs. To obtain wave-induced loading in the seabed (and cyclic shear stress ratios, CSRs), the poroelasticity equations governing the seabed response, coupled with those for fluid and structure domains, are solved simultaneously. Utilizing an experimental model based on anisotropic cyclic triaxial test data that includes CSR and SSR impacts, an equation for the rate of pore pressure buildup is developed and added as a source term to the 2D consolidation equation. Numerical investigations were performed by developing finite element models in time domain. The models were calibrated using particle swarm optimization method and validated against wave flume experimental data. The results indicate that the consideration of static shear stresses has led to sudden rise in residual pore pressures followed by fast dissipations at early and late time steps, respectively, beneath the structure. The exclusion of SSR is shown to cause significant overestimation of pore pressure accumulations at late cycles, potentially causing significant overdesign of MHK foundations. The impact of proximity to the free drainage boundary, CSR amplitude, and loading frequency on the accumulation of residual pore pressure is illustrated. The residual liquefaction susceptibility of the seabed is shown to decline by increase of the seabed slope angle.

Glass-reinforced plastic (GRP) subsea protection covers are widely used to prevent damage to offshore pipelines placed on the seabed from dropped objects, hydrodynamic wave induced loads, and trawling. The light GRP subsea covers could be stabilized by using skirts which penetrate the seabed soil. The dynamic wave pressure acting on the cover will transfer to the cover bottom and the skirt and further influence the pore pressure and seepage flow inside the soil beneath the cover. The present study performs a numerical analysis for the wave-soilstructure interaction (WSSI) of a subsea cover. Two-dimensional (2D) numerical simulations are carried out using an open-source numerical toolbox for modeling the porous seabed interaction with waves and structures under the framework of the finite-volume-method (FVM) based OpenFOAM. The nonlinear waves are solved to obtain the dynamic wave loadings on the cover and the pressure on the seabed. A soil consolidation model is used to provide the initial effective stress in the soil. Then, a one-way coupling algorithm is applied for the WSSI analysis to obtain the soil response in the vicinity of the cover. The distributions of the wave-induced pore pressure, the soil shear stress, and the seepage flow within the seabed are studied and the influences of the wave heights and the skirt lengths are discussed.