Evaluation of the vertical bearing capacity and settlement of bucket foundation in saturated sand

The rapid growth of the demand for renewable energy and the development of infrastructure in offshore area in order to produce the green energy have attracted the attention of many researchers. One of the well-known foundations used for offshore wind turbines is bucket foundation. In this study, the behavior of bucket foundations in saturated sandy soil at different levels of pore water pressure ratios was investigated via physical modeling approach to reach a better understanding of such foundations.
A large soil container of 1.20 m in length, 0.9 m in width, and 0.9 m in height was selected. The Boblosar sand was chosen for experimental tests and is classified as poorly graded sand (SP) categorized by unified soil Classification system (USCS). Excessive pore water pressure could be applied in the soil medium by upward seepage. The problem was investigated for excessive pore water pressure ratios of 0 and 1. Two series of experiments were conducted to study the behavior of bucket foundation under vertical loading. In the first series of experiments, the bucket foundation was loaded by a vertical load in saturated sand without any excessive pore water pressure. Four kinds of bucket foundation were used with different diameters 5, 10, 15, and 20 cm and three different ratios of skirt length to bucket diameter (d/D) were 0, 0.5, and 1. Similar to the first series, in the second series of experiments, the bucket foundation was subjected to a vertical loading at a ratio of saturated sand to excessive pore pressure (ru=∆u/σ). In these experiments, two kinds of bucket foundation with diameters of 10 and 20 cm and different buried foundation depths of 0, 0.5, and 1 were used. The results showed that skirt length and width of the foundation enhanced the bearing capacity of foundation. The bearing capacity of bucket foundation was twice more than the surface circular foundation at both ratios of pore water pressure. By increasing the ratio of pore water pressure, the reduction of bearing capacity of surface circular foundation was greater than that of bucket foundation.