Study of polyphase system mechanical behaviours by a multi-scale approach. Application to unsaturated porous media

Overview & Synopsis

In this thesis, the modeling of the behaviour of the unsaturated porous media is studied in the framework of micromechanics. In order to study the unsaturated case, it is necessary to know the distribution of the fluids in the porous space. The methods permitting to determine the equilibrium positions of a capillary interface inside of a porous medium and to study their stability are presented here, particularly in the case where there is no material exchange between the fluide phases. Then we used the "classical" linear homogenization approach to study the mechanic behaviour for a porous medium saturated by two fuid phases. The results obtained are applied to estimate the drying strains, in the case where the subjected stress and the temperature remain constant, with taking into account the influence of the morphology characters of the porous space and the domains occupied by the fluid phases. The modeling of the behaviour of a medium containing unsaturated mesocracks is studied by considering the coupling between the capillary forces and the geometric changes of the cracks. By an example of drying, we show that, in the case where the cracks are very flat, the macroscopic behaviour accounting for the non-linearity differs significantly from the results of the linear approach. The thesis is finished by an examination of a granular material behaviour. To this end, we use a numerical approach based on the periodic hypothesis of the materials studied. All results obtained in this thesis show clearly the importance to take into account the phenomena existing in the pore scale and the morphologic properties of the domains occupied by each phase in order to modelize the behaviour of the unsaturated porous media.