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A composite bucket foundation (CBF) is a new foundation type of offshore wind turbine. The investigation of the bearing characteristic of CBF is a crucial part of the structural design and safety assessment of offshore wind turbines. This study investigates the bearing characteristic of CBF in sand and clay foundations using centrifuge model test and numerical simulation. Analysis revealed that as load increases, the rotation center of the CBF moves toward the central line and shallow area. The buried depth of the CBF rotation center in a clay foundation is shallower than in a sand foundation when the CBF is under ultimate loading. Due to the rotation and translation of CBF, the soil pressure–depth curves on the skirt wall in different directions will resemble parabolic, line, and triangle shapes, respectively. Under ultimate loading, the relationship between the depth and horizontal coordinate of the rotation center and embedment ratio is linear. The CBF's bearing capacity trend presents quadratic function characteristics as the embedment ratio increases. However, the bearing capacity ratio of the CBF in the clay foundation is faster than that in the sand foundation. The findings provide guidelines for offshore wind turbines. [ABSTRACT FROM AUTHOR]

The properties of coral sands are significantly affected by the gradation changes caused by the particle breakage. In this paper, a series of triaxial consolidated drained (CD) shear tests were carried out to investigate the influence of gradation on the particle breakage and mechanical properties of coral sands. The results showed that the softening and dilatancy during shearing are more significant for coral sands with smaller average particle sizes under low confining pressure. The peak friction angle decreases with the confining pressure and can be fitted by a power function for different gradations. The particle size distribution of the "hyperbolic" or "straight" curve has a trend to transform into a "sigmoidal" type after shearing; and the variation is affected by the confining pressure and the initial gradation. The critical state lines of the coral sands with different gradations are parallel straight lines on the e − (p ′ / p a) ξ plane. In addition, the relative breakage of coral sand particles increases with the confining pressure and the mean particle size. Based on the triaxial compression test results, the expressions relating relative breakages to the confining pressure and the gradation parameters were proposed. [ABSTRACT FROM AUTHOR]