Modifying the Formula of the Ultimate Bearing Capacity of a Shallow Circular Foundation

Abstract

The analytical solution for the ultimate bearing capacity of a circular shallow foundation is studied. The characteristics of existing assumptions, the calculation method, and the yield criterion of the calculation method for the ultimate bearing capacity of a shallow circular foundation are examined. With the assumption that the global shearing deformation surface of the foundation obeys the sliding surface of Prandtl-Reissner’s classic theory, the destruction soil under the foundation is an indeformable rigid-plastic body, and the failure surface obeys the Mohr-Coulomb yield criterion. Based on the static equilibrium condition of the rigid-plastic body and considering the frictional resistance part σtanφ of the failure surface, the theoretical solution for the ultimate bearing capacity of a shallow circular foundation is derived and compared with those of Vesic’s semi-empirical equation and other existing analytic equations. Comparison results show that the bearing capacity coefficients Nc, and Nq can be increased if the frictional resistance part σtanφ of the failure surface is considered, but the variation of bearing capacity coefficient with the internal friction angle of soil are different. Furthermore, the presented theoretical solution, which is a revised calculation method for the ultimate bearing capacity of a shallow circular foundation, is similar to those of Vesic’s semi-empirical equation and other analytic equations.