Seismic Interaction of Offshore Wind Turbines with Tripod Bucket Foundations on Liquefiable Soils Under Wind Loading

The cost-effectiveness and environmental benefits of the tripod suction bucket foundation make it stand out as a preferable option for supporting offshore wind turbines (OWTs) compared to traditional designs like monopile foundations. However, the use of tripod suction bucket foundations in regions with high seismic activity, such as Taiwan, lacks sufficient establishment in current design practices. This study aims to bridge this knowledge gap by investigating the seismic response of a 5MW offshore wind turbine with tripod suction bucket foundations via three-dimensional, fully-coupled, nonlinear finite-element analyses. The analyses showed that earthquake motion increased excess pore water pressure generation, leading to a rise in the excess pore water pressure ratio and, consequently, a decrease in effective stress. The movement of bucket foundations caused by wind loading led to a compressive reaction near the soil on the leeward side, which was observed in the loose sand layer. Furthermore, the presence of wind loading encouraged biases in permanent settlement across the foundation area and the accumulation of soil deformations in the near field, especially in the loose sand layer. This resulted in an accumulation of shear strain parallel to the wind loading direction at the end of shaking. On the other hand, the limited numerical sensitivity study indicated that the magnitude and orientation of foundation rotations were influenced by ground motion characteristics (polarity and velocity impulse) as well as the magnitude and direction of the wind load.Additional research is essential to fully understand the overall impact of velocity impulse and extreme climate loads on offshore wind turbine systems founded on liquefiable soils. A more comprehensive approach involving varied soil profiles, offshore wind turbine foundation configurations, extreme climate load scenarios, and ground motion characteristics is necessary before revised guidelines can be established.

Keywords: Tripod bucket foundations, Liquefaction, Extreme climate loadings, Soil-structure interaction.