A macroelement formulation for shallow foundations on cohesive and frictional soils

The scope of this paper is to present a macroelement model for shallow foundations encompassing the majority of combinations of soil and foundation-soil interface conditions that are interesting for practical applications. The basic idea of the formulation is to raise the common assumption that the surface of ultimate loads of the foundation is identified as a yield surface in the space of force parameters which the footing is subjected to. Instead, each non-linear mechanism participating in the global response of the system is modelled independently and the surface of ultimate loads is retrieved as the combined result of all active mechanisms. This allows formulating each mechanism by respecting its particular characteristics and offers the possibility of activating, modifying or deactivating each mechanism according to the context of application. The model comprises three non-linear mechanisms: (a) the mechanism of sliding at the soil-footing interface, (b) the mechanism of soil yielding in the vicinity of the footing and (c) the mechanism of uplift as the footing may get detached from the soil. The first two are irreversible and dissipative and are combined within a multi-mechanism plasticity formulation. The third mechanism is reversible and non-dissipative. It is reproduced with a phenomenological non-linear hyperelastic model. The model is validated with respect to the existing results for shallow foundations under quasi-static loading tests. It is shown that although the ultimate surface of the foundation is not explicitly used in the formulation of the model, the obtained force states by the model are always contained within it. Copyright (C) 2010 John Wiley & Sons, Ltd.