We propose to work on unsaturated granular materials and in particular on their rheological behavior. We seek to determine the mechanical behavior in the solid and fluid regimes of granular materials in the presence of a non-saturating liquid, which acts through its viscosity and through capillary effects. Such materials, intermediate between dry granular assemblies and highly concentrated suspensions, will be studied experimentally at different scales, from the microstructure to macroscopic behavior. Our goal is to establish the foundations of an understanding of capillary and/or viscous phenomena involved in these materials. A successful modeling scheme of such complex fluids as unsaturated granular materials should be based on a good knowledge of small scale rheophysical phenomena. To this end, the project relies on original experimental characterization schemes of the mechanical behavior of these materials to identify different flow regimes at varying liquid contents, implementing innovative tools providing access to information on their microstructure. The project comprises three parts: a first experimental part (i) seeks to map out the different rheological regimes in the space of control parameters, and should thus determine the density enabling shear flow to be imposed, the yield condition (internal friction, cohesion) of the material, and the critical shear rate and/or strain for which the viscous forces dominate the capillary forces. The second part (ii) involves the development of tools for experimental determination of the microstructure of unsaturated granular materials in the different flow regimes previously established using specific rheometers that can be inserted into imaging devices such as MRI, confocal microscopy and microtomography devices. The third part (iii) of the project consists of grain-scale numerical simulations of granular materials in different deformation and flow conditions, which might involve specific developments. Numerical studies will aim at predicting microstructure and its evolution in terms of the history of deformation and confinement, and will be confronted to experiments. The coupling of parts (ii) and (iii) will lead to the formulation of constitutive laws based on the microstructure, depending on saturation and deformation history. Such microscopic investigations are necessary for two reasons. First, before any continuum modeling, one needs to control density, water content and shear rate homogeneity. Slowly deformed granular materials are prone to shear banding instabilities, which capillary cohesion might favor; water content heterogeneities might couple to those shear-bands. Then, the synergy of experiments and simulations should determine the essential rheophysical mechanisms (rearrangements, formation of clusters…)
Possible applications belong to the field of civil and environmental engineering (mixing of cementitious materials, asphalt, unsaturated soils ...) but may also pertain to other industrial domains (food, pharmacy ...), as well as to geomechanics (landslides, rock joints, fault zones).
Monsieur Abdoulaye FALL (Centre National de la Recherche Scientifique)
The author of this summary is the project coordinator, who is responsible for the content of this summary. The ANR declines any responsibility as for its contents.
CNRS Centre National de la Recherche Scientifique
Help of the ANR 229,932 euros
Beginning and duration of the scientific project: - 48 Months