The accelerating climate crisis has intensified global efforts to develop renewable energy, with offshore wind power emerging as a key solution due to its vast potential and low environmental impact. However, the stability of offshore wind turbines (OWTs) is increasingly compromised by extreme storm events, such as typhoons, which induce strong winds, large wave loads, and seabed liquefaction. While extensive research has been conducted on monopile foundations, most studies focus either on horizontal loads or seabed responses in isolation, lacking a systematic analysis of the coupled pile-soil interaction in extreme storm conditions. This study develops a pilesoil interaction model incorporating pore pressure response to evaluate the stability of monopile and seabed under extreme storm loads. The model is validated using seabed pore pressure models under wave action and monopile response models under cyclic loading. The model is applied to the stability analysis of monopiles at the Cangnan offshore wind farm, where extreme storm loads are quantified using buoy measurement data and incorporated into the model to calculate the responses of both monopiles and seabeds. The results show that the monopile displacement reaches its maximum at the wave crest, and the displacement and moment of the monopile are positively correlated with wave height and negatively correlated with wave length and period. Although changes in wave parameters do not affect the failure mode of the soil, they influence the magnitude and distribution of pore pressure around the pile. The findings provide critical insights into offshore wind turbine foundation stability, offering a scientific basis for improving design strategies to enhance resilience against extreme weather events.

Stiffness degradation of soft clay around offshore monopile is caused by the long-term effect of lateral complex cyclic loading such as wave and wind. Offshore wind turbine structure is a dynamic sensitive structure. It is urgent that the effect of complex cyclic loading on stiffness degradation of soft clay around pile and natural frequency of offshore wind turbine. A series of variable cyclic dynamic shear tests were conducted. The effect of initial shear stress and cyclic shear stress on soften characteristics of soft clay was investigated. It was found that as the initial shear stress is less than the cyclic shear stress, softening index decreases with the increase of cyclic stress ratio. Based on the test results, a soften model of soften clay with considering the effect of initial stress and cyclic shear stress was then built. By combining dynamic motion equation and this soften model of soft clay, a calculation method of natural frequency for offshore wind turbine structure was established to consider the effect of initial shear stress and cyclic shear stress. This method is verified by combining with the results of practical engineering and numerical data. Some parameters influence analysis were performed to explore the effect of amplitude and number of shear stress on the natural frequency of offshore wind turbine structure. The results showed that natural frequency of offshore wind turbine structure decreases with the increase of initial shear stress. As the amplitude and number is increased, the natural frequency decreases.

The mono-column composite bucket foundation (MCCBF) is a new offshore wind turbine foundation suitable for shallow overburden geology. There are few studies on the bearing capacity and deformation of the new subdivided structure 's all-steel MCCBF in layered soil under cyclic loading. This article conducts cyclic bearing characteristics tests on MCCBF in layered soil and shallow overburden layers and studies the ultimate bearing capacity, cumulative rotation angle development rules, and stiffness evolution mechanism. Combined with the finite element analysis results, a calculation method for the ultimate bearing capacity under layered soil is established. The results show that under bidirectional and multidirectional cyclic loading, the ultimate bearing capacity of pure sand changes little, but the strength of clay is reduced, and the ultimate bearing performance decreases. In the clay overlying sand, under high -amplitude cyclic loading, the strength of the sand at the bottom increases, which increases the cumulative angle stiffness and ultimate bearing capacity of the MCCBF. After cyclic loading, the shallow overburden layer will prevent the load from transferring to the deeper soil layer. The foundation will drive the soil in the compartment to slide on the surface of the shallow overburden layer, resulting in a decrease in the load-bearing performance. The initial stiffness of the foundation is increased so that the stiffness change during the cycle is not apparent. Finally, the accuracy of the calculation formula for the ultimate bearing capacity of MCCBF under layered soil is proposed and verified.