Investigating the Response of Tripod Suction Bucket Foundations to Multidirectional Lateral Cyclic Loading-Paper

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The study investigates how tripod suction-bucket foundations for offshore wind turbines respond to monotonic and multidirectional cyclic lateral loading. Because these foundations may vibrate by rocking and experience repeated wind and wave loads, predicting accumulated rotation and deformation is important for design.<br /><br />The authors developed a three-dimensional finite-element model in PLAXIS 3D using the UBC3D-PLM constitutive model, which represents cyclic soil behavior, including densification and pore-pressure generation. They compared predictions with centrifuge tests of a tripod foundation in layered silty sand. In the absence of the laboratory tests normally needed for full model calibration, they used a staged approach: calibrating against an HSsmall model and then adjusting parameters using the centrifuge results.<br /><br />The model reasonably reproduced monotonic behavior and aspects of one-way and two-way cyclic response. However, cyclic stiffness predictions were sensitive to the elastic shear modulus, which depends strongly on soil fines content. The assumed modulus produced a good monotonic fit but appeared to overestimate stiffness during cyclic loading. Two-way loading also revealed differences between the first and later cycles, partly attributable to prior stress history and changes in the number of buckets resisting uplift.<br /><br />The study further found that the interface virtual-thickness setting significantly affected simulated soil–foundation interaction and deformation accumulation. An unsuitable setting could produce unrealistic interface deformations during repeated loading.<br /><br />Overall, UBC3D-PLM appears capable of approximating important monotonic and cyclic behaviors of tripod suction-bucket foundations. Reliable long-term predictions, however, require improved characterization of soil stiffness and careful calibration of cyclic and interface parameters.

Keywords

tripod suction-bucket foundation

offshore wind turbines

monotonic loading

multidirectional cyclic loading

finite-element model

PLAXIS 3D

UBC3D-PLM

cyclic soil behavior

centrifuge tests

soil-foundation interaction