Three-Dimensional Coupled Fem Modelling And Programming Of Partially Saturated Porous Media

The aim of the present work is to create instruments to investigate the mechanical of partially saturated geomaterials, like soils and concrete. The proposed physical – mathematical approach within this manuscript is a coupled thermo-hydro-mechanical model, suitable for consolidation / subsidence analyses of unsaturated soils in view of adapting it also to concrete analysis, possibly under high temperature conditions. This coupled formulation, can therefore be qualified as u – pw – pg – T, by the introduction of basic state variables involved in the processes, that are: the displacements field u, the liquid (water) pressure field pw, the gas (dry air and water vapour) pressure field pg, and the temperature T that is involved in the modelling for non–isothermal processes (this is particularly useful for high temperature and fire conditions). Due to the coexistence of two different fluid phases, liquid and gaseous ones, this model starts from the multiphase approach to a deforming porous medium as proposed by Lewis and Schrefler in the framework of the hybrid mixture theory for porous media, firstly presented by Hassanizadeh and Gray and Zienkiewicz et al. The evolution at macroscopic scale of the above mentioned state variables, in particu-lar of pressures of both liquid and gas, is basically influenced by the microstructure of the material that characterizes the behaviour of geomaterial in relation to capillary effects and de-formability. The physical approach proposed here is based on averaging techniques applied to the physical quantities that can be estimated in a representative elementary volume (REV). With the addition of water retention functions that provide a description of the relation existing among capillary pressure and the degree of water saturation, a complete set of fluid balance equations, mechanical and thermodynamic equilibrium equations can be ob-tained for the medium in a macroscopic scale. The approach and the computation are fully 3D. The starting point of this work is the coupled thermo-hydro-mechanical formulation u – p – T dealing with a fully saturated porous medium, as successfully implemented in the past in the F.E. two-dimensional program PLASCON and its further extensions to three-dimensionality within PLASCON3D. The present work is focused on the extension and upgrading of the single phase theory along with its numerical implementations, towards a more realistic multiphase description of the porous material, where voids may be filled up with both liquid and gas that interacts each other by means of the concept of capillary pressure. An improved code PLASCON3DPS based on the fully coupled u – pw – pg – T formulation developed from previous versions has been performed. Due to the lack in literature of three-dimensional coupled numerical and ex-perimental tests, some numerical results of benchmark tests and real case problems, that derive from two-dimensional domains, are considered for calibration and validation of the novel 3D FEM code.