Undrained Capacity of a Bucket Foundation with a Limited-Tension Interface for Offshore Wind Turbines

In this paper, the influence of the limited-tension interface between lid and soil on the undrained bearing capacity of the wide-shallow bucket foundation is examined by finite element (FE) analysis. The interface between the lid and the soil is modeled using a simplified approach called the surface-based cohesive behavior, with the aim of simulating the limited-tension interface. Initially, the interaction between the lid and the soil is explored under the zero- and unlimited-tension conditions by small-scale experiments. Afterward, the effects of the embedment ratio, soil strength heterogeneity, and lid-soil interface on the bearing capacity are outlined, and the failure mechanisms are explained by FE analysis. A modified closed-form formula is given to compute the moment bearing capacity with the limited-tension interface between the lid and the soil for different embedment ratios and soil strength heterogeneities. The numerical results reveal that the existing approximating solutions, which assume fully bonded interaction, accurately exhibit the shape of the normalized failure envelopes in hm and vh load space for the limited-tension interface. However, the shape of the vm envelopes differs, requiring a novel solution to estimate the combined bearing capacity of the bucket foundation based on the embedment ratio and soil strength heterogeneity with a zero-tension interface between the lid and the soil.