Abstract

The ultimate bearing capacity of shallow foundations subjected to axial vertical loads and resting on soil consisting of two layers has been investigated for the case of strong cohesionless soil overlying weak deposit. In the literature, several theories can be found using simplified failure mechanisms together with a reduced level of the shear strength mobilization on the assumed punching shear zone. It can be reported that large discrepancies between the measured and the predicted values of the ultimate bearing capacities were observed. In this thesis, stress analysis was performed on the actual failure planes observed in the laboratory. In this analysis, full mobilization of the shear strength on the failure planes was considered. New bearing capacity equation was derived as a function of the properties of the upper and lower soil layers, the thickness of the upper layer, the footing depth/width ratio and the angle of the failure surfaces with respect to the vertical. The available experimental data in the literature were used to validate the proposed theory. A design procedure is presented for practicing use.