Vertical bearing behavior and influence depth of the five-bucket foundation for offshore wind turbines in layered soil conditions

The bearing characteristics of the five-bucket foundation (FBF) for high-capacity deep-water offshore wind turbines in layered soil are critical for engineering safety. This research investigated the vertical bearing behavior and influence depth of the FBF in layered cohesive soil foundations underlain by sand strata through numerical simulation. The effects of soil strength ratio (s_{u, top}/s_{u, bottom}) and the distance from the bucket tip to the soil interface (H_upon) on the ultimate bearing capacity, failure modes, and load distribution at the foundation top were analyzed. The influence coefficient of ultimate bearing capacity η and its calculation formula were proposed. Additionally, the failure mode and influence depth (Z) were clarified using the “sand layer probe method”. The results show that the combination of strength ratio and interface depth has a significant impact on the bearing capacity of FBF. A low strength ratio and shallow depth enhance the bearing capacity and promote uniform load distribution at the foundation top. When the strength ratio is less than 1.0, the influence depth of the sand layer decreases to approximately 0.3D (D is the maximum lateral width of the FBF). In contrast, when the strength ratio exceeds 1.0, this depth increases to around 0.7D. Both cases are influenced by H_upon and ultimately converge to a stable value of 0.53D. The research findings can offer theoretical and technical support for the design and bearing calculation of offshore wind power structural foundation engineering.