The influence of superposition and eccentric loading on the bearing capacity of shallow foundations

In 1920 Prandtl published an analytical solution for the bearing capacity of a centric loaded strip footing on a weightless in-finite half-space. Reissner (1924) extended this solution for a surrounding surcharge and Keverling Buisman (1940) for the soil weight. Terzaghi (1943) wrote this as a superposition of three separate bearing capacity components for the cohesion, surcharge and soil-weight. The first question is to what ex-tent the currently used components are correct. The second question is to what extent the superposition is correct, because the failure mechanisms for these three components are not the same. A number of finite element calculations show that there is indeed an error, which is luckily not too large and leads to predictions on the safe side. Meyerhof (1953) extended the equation of Terzaghi with correction factors for the shape of the footing and the inclination of the load. For eccentric loading however, there are no correction factors. The common practice is to reduce the contact area of the foundation such that its centroid coincides with that of the load, which means that, the area of the foundation outside the effective area, is completely neglected. Therefore the third question is, if this reduction of the foundation area is an accurate method to describe the reduction of the bearing capacity due to eccentric loading. A number of finite element calculations show that this is indeed the case.