| dc.description.abstract | Multiphase flow through granular and porous materials exhibits complex behavior, the understanding of which is critical in many natural and industrial processes like infiltration of water into the vadose zone, water dropout in fuel cells, and geological carbon dioxide storage. While fluid–fluid displacement in rigid porous media has been studied in depth, the understanding of the interplay between multiphase flow and granular mechanics remains an ongoing challenge.
Photoelasticity has been used as an experimental technique to quantify the internal stresses within solid bodies for decades, providing numerous microscopic observations in assemblies of circular disks, including contact forces, force-chain lengths and
orientations, that are essential for gaining a deeper understanding of the macroscopic behavior of granular systems. In this Thesis, we extend this technique to producing millimeter-size, residual-stress-free, spherical photoelastic particles that form quasi2D granular assemblies with connected pore space, thus permitting for the first time the visualization and quantification of effective stress in coupled granular-fluid systems. We hereby refer to this novel experimental method as photoporomechanics.
We employ photoporomechanics to study fluid-induced deformation and fracture of granular media, with a focus on its underpinning grain-scale mechanics. For cohesionless granular packs, we uncover two distinct states of the granular pack: a ‘fluidized’ friction-dominated region behind the propagating fracture tips, and a ‘solidified’ elasticity-dominated region ahead of the fracture tips. We then extend the experimental system to study cohesive granular packs, and provide direct observation of the tensile effective stress in the circumferential direction (hoop stress) behind the invasion front, and the compressive effective stress in the radial direction ahead of the invasion front. In each case, we develop macroscopic mathematical models that explain the transition from a fluid-like to a solid-like state underpinning the fracturing process, a phenomenon that plays a key role in real-world processes, such as the drying of superhydrophobic surfaces, the venting of methane from lake and marine sediments, and the formation of desiccation cracks in soils. | |
