Studies on cyclic behaviors of unit bucket for tripod foundation system under various loadings via centrifuge model tests

Offshore wind energy has been growing as a promising renewable energy source. Recently, the tripod suction bucket foundation has been considered as an option to support offshore wind turbines. In an offshore environment, the wind turbine foundation should be designed considering cyclic loading, which can lead to permanent deformation of the structure, tilting, and degradation of soil stiffness. However, there are many uncertainties in the prediction of cyclic behavior of the tripod foundation because the tripod is comprised of three individual buckets embedded into the soil in a triangular arrangement. In this study, the behavior of the tripod foundation under cyclic loadings was indirectly investigated by vertical compression and pullout tests of a single bucket because the overturning moment load 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 a single bucket. In addition, the effects of cyclic loading level were investigated. On the basis of the test results, it was confirmed that the cyclic behavior of the single bucket is significantly affected by loading direction and level. This study highlights that it is important to consider the load characteristics when predicting the cyclic behavior of the tripod.