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 assessment of structures is receiving an increasing interest by virtue of the minimal computational effort required. However, existing formulations commonly neglect any undrained or partly drained soil behaviour, that may be crucially important for simulating the response under dynamic loading. The present study provides an insight into the effects of the hydro-mechanical coupling of the soil on the macroscopic multiaxial cyclic response of shallow foundations. This is accomplished through a series of nonlinear transient analyses on 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 numerical study explores different assumptions for the hydraulic regime, from drained to undrained conditions. The effect of the volumetric-deviatoric coupling on the cyclic response of the reference foundation is examined, highlighting the key role played by the drainage conditions on the stiffness and dissipative features of the foundation system. The effect of non-linearity on the above effects is discussed and interpreted in terms of degradation of the system response at the macro scale.