Study on the combined effects of offshore wind turbine rocking and wave action on transient seabed response near monopile

Offshore wind turbines are frequently subjected to various forms of dynamic cyclic loading throughout their service life, often resulting in pronounced rocking responses of the monopile foundation. To better understand the implications of monopile rocking on seabed stability, this study conducted a series of wave flume experiments to examine excess pore pressure distribution characteristics around a simplified rocking monopile subjected to combined cyclic loading and wave action. A frequency-domain wave energy analysis was employed to investigate the attenuation mechanisms of wave-induced energy propagation within the seabed. Furthermore, a coupled wave-rocking pile-seabed numerical model was developed to simulate the oscillatory response of the surrounding seabed and the evolution of transient liquefaction depth under wave-induced monopile rocking at representative time intervals. Results demonstrate that the use of a fixed monopile model substantially underestimates the liquefaction depth around the foundation. Furthermore, four characteristic alternating-phase scenarios between wave crests/troughs and pile displacement peaks were analyzed to capture phase-dependent stress concentration and liquefaction patterns. The pile-soil interaction significantly modifies the high-frequency energy components of pore pressure fluctuations and alters the seabed natural filtering behavior. The gradient variation of pore pressure in the shallow strata is shown to be strongly influenced by the rocking motion of the monopile.