Identification, implementation, and validation of a macro-element for the cyclic response of shallow foundations in saturated soils

Under seismic loading, the cyclic behavior of shallow foundations in saturated soils is significantly influenced by the development of excess pore water pressures, as evidenced by a number of experimental and numerical results. However, there is still a lack of computational tools that are capable to describe this phenomenon and are at the same time applicable in soil-structure interaction analyses. In a macro-element approach, the foundation behavior is reproduced through a macroscopic constitutive law, relating generalized forces acting on the foundation to generalized foundation displacements. The present work incorporates into a macro-element for shallow foundations the detrimental effects of the development of excess pore water pressure induced in the foundation soil by the cyclic seismic actions. This is accomplished by implementing a recently formulated model, called TIM-UP, and validating this model against results obtained with a full three-dimensional finite element model of a cyclically loaded shallow foundation, developed in OpenSees. The potentiality of the model is then demonstrated by simulating irregular multiaxial loading paths under different drainage conditions.