Numerical Simulation of Vertical Cyclic Responses of a Bucket in Over-Consolidated Clay

Multi-bucket foundations have become an alternative for large offshore wind turbines, with the expansion of offshore wind energy into deeper waters. The vertical cyclic loading-displacement responses of the individual bucket of the tripod foundation are relevant to the deflection of multi-bucket foundations and crucial for serviceability design. Finite element analyses are used to investigate the responses of a bucket subjected to symmetric vertical cyclic loading in over-consolidated clay. The Undrained Cyclic Accumulation Model (UDCAM) is adopted to characterize the stress-strain properties of clay, the parameters of which are calibrated through monotonic and cyclic direct simple shear tests. The performance of the finite element (FE) model combined with UDCAM in simulating vertical displacement amplitudes is evaluated by comparison with existing centrifuge tests. Moreover, the impact of the bucket's aspect ratio on vertical displacement amplitude is investigated through a parametric study. A predictive equation is proposed to estimate the vertical displacement amplitudes of bucket foundations with various aspect ratios, based on the cyclic displacement amplitude of a bucket with an aspect ratio of unity.