Noémie Prime

Unified model for geomaterial solid/fluid states and the transition in between

AbstractDuring mudflows, geomaterials evolve in a very specific manner, because initially they behave as solids, and then they turn to flow as viscous fluids. This paper proposes an original approach to simulate, within a single numerical framework, such a transition between a solid-like and a fluid-like behavior. The model used is based on the association of an elastoplastic and a viscous constitutive relation to describe both phases of the behavior. The transition between the two is assumed to correspond to a failure state, and the transition criterion considered is thus based on the general second-order work stability criterion. The Plasol elastoplastic model and the Bingham viscous model are used because they are suitable to describe soils and granular suspensions, respectively. In this preliminary study, the global model is tested for two homogeneous loading paths with drained and undrained conditions. For these cases, the radical transformation of the material behavior at failure is captured, and bo...

On Water Transfer and Hydraulic Connection Layer During the Convective Drying of Rigid Porous Material

The convective drying of a natural porous material, limestone, is investigated in this study, with both experimental and numerical approaches. The first experimental campaign, which focuses on the influence of samples’ slenderness, suggests the presence of a hydraulic connection layer between the porous water and the external environment, in spite of the very fine pore structure of the material. This hydraulic transfer enables the fast water evaporation at the beginning of the drying test, when external conditions drive the kinetics. Furthermore, the results show that this layer does not exceed 30 mm deep from the external surface, given the drying conditions of the test. A second experimental campaign aims to analyse, by mean of an X-ray tomography tool, the internal water content during the drying. It confirms that water transfer takes place within the limestone in two distinct stages. The first stage being faster than the second one with a homogeneous desaturation along the sample, it is consistent with the hypothesis of the hydraulic connection layer. Finally, the finite element modelling makes possible to identify the main mechanisms of water transfer, namely liquid convection and vapour diffusion.

Experimental Investigation of Hydromechanical Coupling During Clay Drying

Boom clay is studied as a potential host rock for underground nuclear waste storage. This experimental work analyzes its response under the convective drying conditions that may be applied in case of contact with the ambient atmosphere (during disposal drilling, for instance) or with gallery ventilation (because of damage in gallery lining). The drying kinetics is first established. In a second phase, the cracking and shrinkage onset and development are focused on, thanks to an X-ray microtomography device. The results show a phase of ideal shrinkage and a phase of shrinkage with desaturation, which are closely related to the kinetics. Cracking and shrinkage progressively develop from the drying surface, up to values representing about 3 and 12% of the cross section area, respectively.