Thermo-Elasto-Plastic Consolidation Analysis with Water Phase Change

The aim of this work is the numerical study of the thermal consolidation process in the framework of coupled thermo-hydro-mechanical (THM) behavior of soils including water phase change. In recent years, increasing interest in thermo-hydro-mechanical analysis of saturated and partially saturated porous materials is observed, because of a wide spectrum of their engineering applications. An area of particular interest is Environmental Geomechanics, where some challenging problems are of interest. Examples are subsidence above gas reservoirs, injection of other fluids into deep or superficial aquifers, long-term storage of carbon dioxide, problems linked with soil failure such as the onset of flowslides and catastrophic landslides, problems connected with nuclear and other hazardous waste disposal and geothermal structures or groundwater. In all the aforementioned situations, the soil or rock need to be considered as multiphase porous medium in isothermal or non-isothermal conditions, made of a solid phase and voids containing one or more fluids, in which the interaction between all the components of the material cannot be neglected. In case of liquid and gaseous fluids, capillary effects cannot be a priori neglected, and also phase change for liquid water and its vapor can play a role. For enabling significant predictive simulations to be carried out, suitable physical and mathematical models have to be developed. Then, coupled Thermo-Hydro-Mechanical (THM) finite element codes are of paramount importance for simulation and analysis of geo-environmental engineering problems. A step in the development of a suitable physical, mathematical and numerical model for the simulation of geo-environmental engineering problems is presented here. To this end, the general ACMEG-TS thermo-elasto-plastic constitutive model for saturated/unsaturated clayley soils, has been implemented in the finite element code COMES-GEO for the analysis of non-isothermal saturated/partially saturated deformable porous materials. The numerical model is based on a fully coupled heat and multiphase flow model in deforming porous media. The porous medium is assumed to be a multiphase system where interstitial connected voids of the solid matrix may be filled with liquid water, water vapor and dry air. The general frame of averaging theories has been used in deriving the governing equations. Phase changes of water (evaporation-condensation, adsorption-desorption) and heat transfer through conduction and convection, as well as latent heat transfer are considered. The elasto-plastic behavior of the solid skeleton is assumed homogeneous and isotropic; the effective stress state is limited by the temperature and capillary pressure dependent ACMEG-TS yield surface. The governing equations are discretized in space and time by means of the finite element method. The numerical examples will show applications of the full set of equations. Coupled heat, water and gas flow in deforming porous media are validated against existing numerical solutions. The non-isothermal elasto-plastic consolidation of a soil column of Boom clay loaded by thermal, mechanical or environmental conditions is studied in detail, aiming to analyze the effects of the environmental loads on this material candidate for an underground nuclear waste storage facility. A case where the temperature is above the bowling value and water phase change develops is also studied