Numerical Investigation on the Static Lateral Bearing Capacity and Failure Mechanism of Pile–Bucket Foundation

The pile–bucket foundation, comprising a bucket attached to a single pile, represents an innovative offshore solution for supporting wind turbines. Previous studies on laterally loaded foundations have primarily focused on single piles and pile–bucket systems; however, the effects of bucket size and loading eccentricity on lateral capacity and soil failure mechanisms remain insufficiently understood. This study investigates the lateral performance of pile–bucket foundations in silty sand under static loading conditions. Seven three-dimensional numerical simulations were conducted to evaluate the influence of bucket diameter, embedment depth, and loading eccentricity. Results indicate that pile–bucket foundations achieve 37–60% higher lateral capacity than single piles and 3–4 times the capacity of standalone buckets. Increasing bucket diameter produces more significant improvements than increasing embedment depth, whereas higher loading eccentricity reduces lateral capacity, ranging from an 8% increase to a 10% decrease relative to a single pile. Increases in loading eccentricity, bucket diameter, and embedment depth shift the rotation center upward by approximately 3–9%, compared with a single pile. At the mudline, the bucket resists up to 75% of the lateral load, while the pile carries up to 92% of the moment. Failure mechanisms are dominated by excessive rotation, including wedge-type failure near the mudline and deep rotational soil flow. Increasing bucket diameter or embedment depth raises bending moments by 5–9%, while higher eccentricity amplifies them by 32–50%. A modified analytical formulation incorporating a correction factor of 1.16 improves the prediction of the rotation center position. These findings provide quantitative guidance for the design and optimization of pile–bucket foundations supporting offshore wind turbines.