Influence of Soil Type and Load Eccentricity on the Static Lateral Behavior and Failure Mechanisms of Pile–Bucket Foundations

For offshore wind turbines, pile–bucket foundations enhance lateral resistance by mobilizing both shallow and deep soil resistance mechanisms. However, the combined influence of soil conditions and load eccentricity on their lateral performance has not been fully investigated. This study employs three-dimensional finite element simulations to examine the lateral behavior and failure mechanisms of pile–bucket foundations subjected to eccentric loads in three soil types: medium sand, silty sand, and medium clay. The results show that the lateral capacity of the pile–bucket system exceeds that of a single pile by approximately 19.4% in medium sand, 37% in silty sand, and 64% in medium clay. Compared with a standalone bucket foundation, the pile–bucket offers roughly 5.7, 4.0, and 3.0 times greater capacity, respectively. Increasing load eccentricity reduces the lateral bearing capacity by approximately 20–34% across all soil conditions. It also causes the rotation center to migrate upward by about 4–7% in medium sand and silty sand and by 6–8.5% in medium clay. Furthermore, the lateral load-sharing ratio decreases by approximately 6–13% in medium sand, 10–22% in silty sand, and 15–37% in medium clay, whereas the moment-sharing ratio increases slightly by about 2–3% in medium sand and silty sand and by 2–4% in medium clay. Under all soil conditions, the foundation exhibits a rotation-dominated failure mechanism characterized by deep rotational soil movement and wedge-type deformation near the mudline. Although eccentric loading affects the lateral response, the overall failure pattern remains unchanged. These findings provide new insights into how eccentric loading and soil conditions influence the lateral behavior of pile–bucket foundations.