Évolution de la microtexture d’une matrice kaolinitique sur chemin triaxial axisymétrique

The goal in this work is to understand how the microfabric of a kaolinitic matrix evolves when it is submitted to an axisymmetric triaxial loading path. The approach consists in doing a triaxial test on slightly overconsolidated saturated specimens, then to follow the microstructure changes (orientation of the clay particles and porosity) during the test using scanning electron microscope observations. In the initial state, the clay is consolidated under oedometric conditions and the observations show an anisotropy of the microfabric with a preferential orientation of the particles according to the horizontal plane perpendicular to the direction of the loading. On an isotropic path, the analysis shows a progressive reorientation of the particles towards a more isotropic fabric. This evolution continues at the beginning of the triaxial loading, whereas the particles tend to become preferentially oriented along an inclined plane at the end of the loading. The evolution of the porosity is derived from mercury intrusion porosimetry tests, confirmed by SEM photograph observations. The results suggest the existence of a double porosity in the initial state of the specimen. This double porosity seems to be maintained during the isotropic loading, then evolve towards a unimodal porosity, with a slight decrease in the pore size, during the triaxial loading.