Analysis of cylindrical and rectangular bucket foundations subjected to vertical and lateral loads in sand using a three-dimensional displacement approach

Abstract

One of the major concerns in designing bucket foundations is addressing the effect of the shape of the foundation on deformation. It has not yet been clarified sufficiently how the ultimate load capacity and the deformation up to failure are dependent on the bucket shape, bucket dimensions, loading conditions, and soil properties. Not only for conventional cylindrical bucket foundations, but also for rectangular bucket foundations, in order to adequately design each type of bucket foundation, analytical solutions for the general loadings of both foundations have been urgently needed. In the present paper, analytical solutions are provided by a three-dimensional displacement approach for predicting the deformation up to failure of the soils surrounding cylindrical and rectangular bucket foundations subjected to vertical, lateral, and moment loads in cohesionless soils. The analyses are carried out for nonhomogeneous sandy soils. The lateral stiffness coefficients along the short skirt are presented by extending those along the normal skirt for both cylindrical and rectangular bucket foundations. The lateral yield along the skirt and the compression and shear failures below the base in sand are seen to have a significant influence on the ultimate lateral and moment load capacities of cylindrical and rectangular bucket foundations under vertical loads. Failure envelopes expressed by both ultimate horizontal and moment load capacities under various vertical loads in sand are presented. For cylindrical bucket foundations, as the embedment ratio and vertical load increase, the ultimate lateral and moment load capacities increase. However, for rectangular bucket foundations, the relationships among the ultimate lateral and moment load capacities, vertical load, and embedment ratio are greatly influenced by the breadth ratio. The largest ultimate lateral and moment load capacities among the breadth ratios of rectangular bucket foundations under a certain vertical load depend on the embedment ratio. The ultimate lateral and moment load capacities of square bucket foundations are less than those of cylindrical bucket foundations with the same cross-sectional area. The predicted relationships between the ultimate lateral and moment load capacities and the embedment ratio under various vertical loads are compared with the results obtained from FEM and experiments. The monotonic behavior of the sand surrounding bucket foundations up to failure is elucidated from the relationship between the lateral load and the lateral displacement and that between the moment and the rotation.