Résumé
Desiccation cracking is one of the modes of failure of geomedia that has been rarely addressed from the point of view of its multi-phase, multi-physics and multi-scale complexity. In fact, several elements of drying-cracking process and their coupling are still quite poorly understood. The list of phenomena contributing to drying cracking include: evaporation of surficial pore water, evaporation of capillary water and possibly adsorbed water in clay, transport of water and vapor through pore space, air entry, displacement of water/air interface and its dynamics, evolution of suction, suction resultant force and surface tension force, deformation of the pore space/solid skeleton due to suction/pressure evolution intergranular force evolution during drying, drying shrinkage, constrained drying shrinkage and the effective stress evolution due to it, air entry, onset and development of drying cracking, evolution of the drying crack systems, evolution of permeability of drying crack systems. The presentation will present some of new experimental results concerning the aforementioned mechanisms. For small granular assemblies, the main findings include intermittent slow, evaporation rate driven fluid motion, associated with modest pressure gradients, and fast, non-equilibrium driven re-configurations of liquid/gas interfaces (Haines jumps). Within a single two-grain bridge numerical simulations suggest a consistent flow of liquid from the central area of the bridge, axially toward the solid contact, and then along the solid interface toward the contact area. The flow is believed to contribute to contact pinning. Pinning is viewed as one of the precursors of capillary bridge rupture. Micro-scale experiments on evaporating hydrophilic grain clusters show that their cohesion controlled by the adhesion-forces. The adhesion-force is composed of capillary pressure force acting over the liquid/solid contact surface area, and surface tension forces acting over the three-phase contact perimeter length. This is in contrast with most macro-scale phenomenological models, in which the only desaturation process variables affecting strength are suction and saturation. In reality, both the contact surface area and contact perimeter length are reduced to zero upon complete liquid evaporation.