Centrifuge modelling of drained pullout and compression cyclic behaviour of suction bucket

In recent years, the tripod suction bucket foundation has been considered as an option to support offshore wind turbines. In an offshore environment, a wind turbine foundation should be designed considering cyclic loading, which can lead to the permanent deformation of structures, tilting and the degradation of soil stiffness. However, there are several uncertainties in the prediction of the cyclic behaviour of the tripod foundation, since the cyclic horizontal, vertical and moment loadings applied on each bucket lead to a complicated mechanism for each bucket. In this study, the behaviour of the tripod foundation under cyclic loadings was indirectly investigated through the vertical compression and pullout tests of the bucket because the overturning moment applied to the tripod foundation presumably acts as vertical compressive and pullout loads on each bucket. A series of centrifuge model tests were performed by applying one-way (i.e. vertical compression and pullout) and two-way cyclic loadings to the single bucket. Additionally, the effects of cyclic loading level were investigated. It was confirmed that the cyclic behaviour of the single bucket is significantly affected by loading direction and level. This study highlights the importance of considering load characteristics when predicting the cyclic behaviour of the tripod.