Effect of the external beveled tip angle of the bucket foundation in clay on its penetration resistance considering soil large deformation and strain softening

Abstract

In offshore wind energy industry, the bucket foundation in clay has been considered as an alternative to conventional foundations due to their unique features such as high overturning resistance. However, it cannot be installed to the pre-determined depth due to the soil plug generated during the penetration, which will significantly affect its bearing capacity. By setting the external beveled tip at the bottom of the bucket, the height of the soil plug can be reduced effectively. In order to study the influence of external beveled tip on the soil plug, soil softening and penetration resistance, the Coupled Eulerian-Lagrangian approach is used in this study to establish the bucket foundation penetration resistance models in correlation with different angles of external beveled tip considering soil large deformation and strain softening. It was found that as the angle increases, more soil are directed and flows out of the bucket, and the height of soil surface inside the bucket obviously decreases. When the angle increases to 60°, the soil plug inside the bucket is very small and hardly changes. As the angle increases from 0° to 60°, the degree of softening and amount of soil inside the bucket decreases, while that the trend is opposite for the soil outside the bucket. In addition, due to the influence of soil flow and strength degradation, the end bearing capacity factor and the frictional coefficient of inner side wall decrease as the angle increases, while the coefficient of outer side wall increases due to the reduction of softening effect. However, the total penetration resistance of the bucket foundation does not obviously change with the external beveled tip angle. 60° is recommended as the optimal angle for the external beveled tip in order to avoid the soil plug inside the bucket.