Rheology of dry, partially saturated and wet granular materials

This thesis is dedicated to the study of the rheology of dry, wet and partially saturated granular materials. Granular media, suspensions, emulsions, polymers and gels are ubiquitous in the chemical and materials processing industry, and despite their very different appearance, the rheology and study of the behaviour of these materials is the key to the large-scale industrial production.
Granular materials are large collections of discrete particles. A granular material is called dry if the fluid in the interstices or voids between the grains is a gas, which is usually air. For dry granular media, the dominant interactions are inelastic collisions and friction, which are short range and non-cohesive. If the voids are completely filled with a liquid, the material is called a saturated granular material. If there is a liquid in some of the voids, and the rest of the voids are filled with a gas, the material is said to be partially saturated. Surprisingly, adding a small amount of liquid to granular matter transforms its properties because the liquid induces a cohesion between the grains. Cohesion in wet granular media arises from the surface tension and capillary effects of the liquid. The mechanical properties at low water contents are determined by the liquid bridges between grains, and those at high water content are determined by the flow of the liquid through the soil pores.
We aim here to study the behaviour of granular materials in different regimes of wetness. We have investigated the flow, stability, optimum strength, time reversibility and other rheological behaviour of these systems (dry, partially granular materials and suspensions) in different experiments.