Numerical analysis of the mechanical interaction among adjacent foundations: towards a simplified design approach

The increasing demand of sustainability of the construction of new structures and the necessity of verifying/retrofitting the existing ones require reliable design tools. To this aim, fundamental is gathering new insights in the mechanical response of foundations. As far as shallow foundations are concerned, one aspect commonly disregarded in the current engineering practice is the influence of the mechanical interaction among adjacent foundations. The authors approach this problem by performing a parametric finite element non-linear numerical study on a squared shallow foundation, loaded by a vertical centred load under fully drained conditions. The numerical results put in evidence that the interaction, for any spacing value, causes an initial increase in settlements, whereas the dependence of bearing capacity on spacing seems to be, according to the case, either beneficial or detrimental. For particular geometries and mechanical properties, the reduction in bearing capacity may reach about the 30%. These dependences are justified in the light of the findings at the local scale, i.e. discussing the spatial distributions of irreversible strain, displacement and stress fields as the applied load increases. Finally, the authors have proposed a simplified design approach to derive not only the bearing capacity, but also a preliminary prediction in terms of displacements accounting for the reciprocal foundation interaction.