A Generalized Constitutive Relationship for Undrained Soil Structure Interaction Problems

The macroelement approach, commonly employed to study soil-structure interaction problems, stems from the intent of describing the mechanical response of a complex system by means of a single upscaled constitutive relationship, relating generalized stresses and strains. In this paper, the authors introduce a new generalized constitutive relationship capable of reproducing the undrained mechanical response of both foundations and tunnel cavities. To this aim, the authors performed a series of numerical analyses. The numerical analyses results are interpreted to put in evidence that the mechanical response of both systems is governed by a “structural hardening” associated with the spatial propagation of the yielded soil domain that is influenced by the relative position of the structure with respect ground surface: when the yielded soil domain reaches the ground surface a failure condition is got. To take into account this aspect, the authors introduced in the constitutive relationship two independent plastic mechanisms, the former one defines the spatial propagation of the yielded soil domain (structural hardening), whereas the latter one the failure mechanism due to the boundary condition. The comparison of the constitutive relationship predictions with the finite element numerical data demonstrates that the proposed model is capable at the same time of satisfactorily reproducing the mechanical response of shallow/deep tunnels and shallow/embedded foundations.