Design of piled-raft foundations by means of a multiphase model accounting for soil-pile interactions

The settlement behavior of a pile-raft foundation is analyzed with the help of a multiphase model aimed at describing the overall response of the reinforced ground. According to this model, the group of piles is treated as a homogenized continuous medium in interaction with the soil along the pile length, as well as at their lower tips. These two kinds of interaction, which play a decisive role in the way the piles are actually working as strengthening elements, are described by specific constitutive laws which can be directly introduced in the general governing equations of the multiphase model. Thus improved, the multiphase model can then be incorporated in a finite element code developed in the context of an elastoplastic behavior of the soil, provided that the constitutive parameters of the interaction laws have been previously identified. This identification procedure is performed through numerical simulations of the simple problem of a single pile, loaded at its top. The global response of vertically loaded piled-raft foundations, expressed in the form of load settlement curves, is finally presented, clearly highlighting the decisive influence of the mobilized pile shaft friction and tip resistance on the foundation settlement reduction.