Upscaling Process Towards a Unified Thermodynamic-Based Multi-Physics Inertial Macroelement for Geotechnical Systems

The response of a geotechnical system, be it a foundation or a bridge abutment, is controlled by mechanisms occurring at different scales, i.e. the behaviour of the soil microstructure, the contact stresses exchanged between soil and structural members, the interaction of the soil skeleton with the pore fluid. In this study, a thermodynamic formalism, termed TIMg-UP, is proposed to predict soil–fluid–structure interaction at the macroscopic scale of the geotechnical system. Emphasis is given on some long-standing issues, related to the dependence of the multiaxial response of geotechnical systems on the hydro-mechanical coupling of the soil behaviour and on the load frequency. The resulting evolution of the mixed hardening response of the TIMg-UP is controlled by an internal variable accounting for the level of drainage of the pore water. A complementary damage variable simulates degradation of the macroscopic features induced by the pore water pressure build-up at the meso-scale. These effects are then combined with the inertial ones developing in the soil under dynamic loading, leading to a unified macroelement linked to meso-scale characteristics. The TIMg-UP is tested under different conditions, pointing out its potentiality to renew design and assessment of bridges and buildings at the territorial scale.