Failure envelope and bearing capacity of a rigid ring footing on sand layer overlying stiff clay under eccentric loads

In this paper, numerical calculations in axisymmetry based on the finite difference method are carried out to calculate the bearing capacity of a rigid ring footing on sand overlying stiff clay subjected to eccentric loading. The verification of the model accuracy is examined after an initial analysis by comparing the bearing capacity factor N γ of a rough and smooth circular footing loaded vertically and placed on the surface of the soil. To show the effect of eccentricity, sand layer thickness and friction angle, the results are presented in graphs and normalized failure envelopes in the V-M loading plane. The results indicate on one hand that the eccentricity of the load has little effect on the reduction of the bearing capacity as long as this eccentricity remains less than the third of footing width, on the other hand, that the influence of the clay layer on the increase of the bearing capacity is negligible if the thickness of the sand layer exceeds twice of the footing width. Moreover, the friction angle makes a significant difference to the size of the standardized failure envelope.