Upper Bound Solution of the Resisting Moment Bearing Capacity of A Composite Bucket Shallow Foundation of An Offshore Wind Turbine in Sand

Bearing the large moment that is generated by the wind load that acts on the upper structure of offshore wind turbines is an important feature of their foundations that is different from other offshore structures. A composite bucket shallow foundation (CBSF) has been proposed by Tianjin University to address the soft geological conditions in the offshore regions of China for wind turbines. The CBSF is a new type of foundation and is effective against large moments. The soil deformation test of a CBSF and the numerical simulation study under the same working conditions are carried out to determine the failure mechanism of a CBSF under moment loading. The resisting soil compression rate ηm is defined as a new empirical parameter that indicates the ability of the soil inside the bucket to resist moment loading. The upper limit of the resisting moment bearing capacity of the bucket foundation is derived through the upper bound theorem of classical plasticity theory based on the failure mechanism. The calculation method is validated by tests of bucket models with different height-diameter ratios in sand under moment loading.