Local scour influence on horizontal bearing behavior of offshore wind bucket foundations: An experimental study

Local scour can significantly degrade the horizontal performance of offshore wind bucket foundations, yet its post-scour response remains insufficiently understood. This study conducted model tests on bucket foundation to investigate its horizontal bearing behavior, failure characteristics, and H-M failure envelope under scour. Based on Froude similarity, the effects of scour depth, loading direction, and combined horizontal-moment loading were examined. The normalized horizontal ultimate capacity decreased from 1.722 without scour to 1.559, 1.396, and 1.163 at scour depths of 0.1D, 0.2D, and 0.3D, respectively. The reduction was approximately linear within 0-0.2D, and reached 32.46% at 0.3D. After scour, downstream-side loading produced a larger ultimate capacity than upstream-side loading, owing to the distinct scour pit on the upstream side and slight deposition downstream. Scour also reduced the initial stiffness, intensified displacement development, promoted an earlier transition to pure rotation, and shifted the stable rotation point downward. Under combined loading, the H-M failure envelope remained approximately elliptical, but became markedly narrower after scour. A dimensionless envelope expression was fitted for both conditions. The results provide an experimental basis for evaluating the post-scour horizontal performance of bucket foundations and for improving their engineering design.