Influence of the superposition and flow rule assumptions on the bearing capacity of shallow strip footings

A rigorous solution aimed at accounting for the superposition and flow rule assumptions in the assessment of the bearing capacity of shallow strip footings under plane strain conditions has been developed using the method of characteristics and the finite element method. With reference to the Hill and Prandtl failure mechanisms, a bearing capacity factor N gamma q and a superposition corrective coefficient mu that allow to directly obtain the actual bearing capacity of shallow strip foundations have been proposed. The geometry of the plastic volume involved in the failure mechanism has been also investigated, highlighting the influence of the superposition and flow rule assumptions. Starting from the numerical results obtained using the method of characteristics, several empirical relationships have been proposed for an accurate estimate of N gamma q and mu as well as for the lateral extension and depth of the plastic volume. The accuracy of the numerical results has been checked through finite element analyses under the assumption of associated and non-associated flow rule showing that the proposed superposition corrective coefficient mu is not influenced by the flow rule assumption. Thus, a general bearing capacity equation for shallow strip footings has been provided which accounts for superposition approximation and non-associated flow rule.