A simple equation for bearing capacity of a shallow foundation

The bearing capacity of a shallow foundation is likely found from the application of various correction factors (for foundation shape and embedment, load inclination and eccentricity, and the inclination of the foundation base) to a three term bearing capacity equation that contains bearing capacity factors Na, Iq and Nc, which differ depending on the classical source consulted (Terzaghi, Meyerhof, Hansen or Vesic). Unfortunately, there have been very few full scale tests that have documented the accuracy of such equations causing considerable uncertainty in the mind of the practicing engineer. Complicating factors that lead to confusion regarding the meaning and application of the assessed bearing capacity are the choice of total or effective stress strength parameters, the use of direct shear, triaxial or plane strain friction angle for cohesionless material, the effect of confining pressure variation in different zones of the failure mass on the chosen angle, and the effect of apparent cohesion, particularly in the interpretation of plate load test results. This thesis provides discussion and illustration of these various matters, including the introduction of a much simpler bearing capacity equation that can also yield load-settlement response. In this case, the so-called bearing "capacity" can be assessed based on whatever "failure" criteria the user chooses to use (e.g. load/pressure at 1.0 inch displacement, or at a displacement equal to a percentage of the foundation width or for a given slope on the load-settlement curve). The accuracy of proposed equation is verified using the available full scale field tests on shallow foundations.