Vertical bearing capacity of circular surface foundations considering the effect of compactness and stress level on the sand friction angle

The vertical bearing capacity of circular surface foundations is the key to calculating that of suction caissons, and the latter is generally expressed as a multiple of the former. In the existing research, the soil around shallow foundations is considered homogeneous, and the sand friction angle is constant. In fact, the friction angle is affected by the compactness and stress level. For sand with a certain relative density, the friction angle varies with the soil depth. Therefore, a method, considering the effect of compactness and stress level on the friction angle, is proposed to calculate the vertical bearing capacity of circular surface foundations. Compactness and stress level are characterized by relative density and soil depth, respectively. The main innovation of this method is that the relationship between the friction angle, relative density, and soil depth is obtained, and the friction angle is expressed as a function of relative density and soil depth. This varying friction angle, after proper handling, can be used for vertical bearing capacity calculations. Combined with an example, the applicability of this method is verified. The research shows that the calculated results are in good agreement with the test results when the appropriate basic parameters are determined.