Pullout capacity of suction bucket foundations considering drainage conditions

Abstract

Tripod bucket foundations have been identified as a feasible foundation to support offshore wind turbine structures. The structure is subjected to horizontal load due to wind and wave forces. The imposed load induces a push and pull mechanism which governs the capacity of the overall system. The bearing capacity of the foundation is relatively large while the pullout capacity is rather limited. The pullout of a single bucket in a tripod system determines the overall stability and requires investigation in order to satisfy the applicability. Therefore, a series of 1-g experimental tests were conducted on model suction buckets to evaluate the pullout capacity affected by the drainage conditions. The drainage conditions during failure were varied by applying different loading rates and aspect ratios of the model bucket. Resistance to pullout forces and variation of suction pressure during failure is analyzed in detail. A simple approach is proposed to estimate the pullout capacity for preliminary design purposes. Also, a drainage factor was proposed based on the model test to classify the drainage condition during pullout.