On the dynamic response of shallow foundations in saturated soils

In recent years, the development of macroelement approaches to include the macroscopic nonlinear response of soil-foundation systems in the seismic assessment of structures is receiving an increasing interest by virtue of the minimum computational effort required. However, existing formulations commonly neglect any undrained or partly drained hydraulic condition. This study aims at providing an insight into the effects of the hydro-mechanical coupling of the soil on the multiaxial dynamic response of shallow foundations. This is accomplished through an incremental dynamic analysis of a fully coupled soil-foundation numerical model implemented in OpenSees, providing an explicit description of the pore water pressure build-up induced by the nonlinear soil behaviour. The dynamic analyses were carried out exploring different assumptions for the hydraulic regime, from drained to fully undrained conditions. A broad range of frequencies of the harmonic input motion was investigated to highlight the influence of the hydro-mechanical coupling on the frequency- and amplitude-dependant response of the foundation. Dynamic amplification curves for the considered soil-foundation system are presented, leading to the identification of its dynamic features from small strains to a high level of mobilised strength in the soil. Preliminary indications are provided about the inclusion of the effects above into a macroelement approach recently developed by the authors.