Cyclic behaviour of unit bucket for tripod foundation system under various loading characteristics via centrifuge

Offshore wind energy has been growing up as a promising renewable energy source. In recent, tripod suction bucket foundation, which is consisted of three buckets, is rapidly expanding as a foundation system supporting the offshore wind turbine. In offshore environment, wind turbine foundation structures should be designed considering cyclic loading which can lead to permanent deformation of structure, tilting problem and overall degradation of soil stiffness. However, it is technically difficult to predict the cyclic behaviour of the tripod accurately, but the good thing is that the cyclic behaviours of the tripod bucket can be inferred from vertical pullout and compression behaviours of each single bucket elements. In this paper, a series of centrifuge tests was performed by applying cyclic vertical compression and extension loadings to a single bucket element that is one element of the tripod foundation. Loading directions and level were controlled for investigating of cyclic behaviour of tripod foundation. On the basis of testing results, the permanent deformation and cyclic stiffness response of tripod suction caisson were discussed. Based on the test results, it was confirmed that the cyclic behaviour of the single bucket is affected by the load level. In addition, the behaviour showed quite different trends with the loading directions: compression; pullout; and two-way.