Three-dimensional modeling of wave-induced residual seabed response around a mono-pile foundation

Recently, behavior of large-diameter mono-pile foundations for offshore wind turbines under long-term cyclic wave loading has attracted great attentions from coastal engineers. In this study, a three-dimensional integrated numerical model is developed to investigate the wave-induced seabed response around a monopile foundation. In the model, the Reynolds-Averaged Navier-Stokes (RANS) equations are used for the mean fluid flow, while the Biots consolidation equations are used for the solid-pore fluid interaction in a porous seabed. The monopile is considered as a single phase medium and behaves under a linear elastic law. To reproduce the residual soil behavior under cyclic shearing induced by ocean waves as well as structural rocking motions, a poro-elastoplastic model is adopted, in which the consolidation analysis of seabed foundation under gravitational forces including the body force of structure is pre-assessed and incorporated. The present numerical framework was first validated against several laboratory experiments and obtaining fairly good agreements. Based on the proposed model, failure of monopile foundation caused by liquefaction due to the buildup of pore water pressure under cyclic shearing is investigated. Numerical results indicate that the potential areas for residual pore pressure development and the resulting liquefaction are most pronounced in the vicinity of the monopile following the wave propagation direction, which is caused by waves as well as the rocking motion of the structure induced by the wave impact. Parametric studies indicate that there is no possibility of generating soil liquefaction below the pile bottom in the vicinity of the mono-pile even under large waves.