Recent theoretical and experimental work suggests a frictionless-frictional transition with increasing inter-particle pressure explains the extreme solid-like response of discontinuous shear thickening suspensions. However, analysis of macroscopic discontinuous shear thickening flow in geometries other than the standard rheometry tools remain scarce. Here we use a Hele-Shaw cell geometry to visualise gas-driven invasion patterns in discontinuous shear thickening cornstarch suspensions. We plot quantitative results from pattern analysis in a volume fraction-pressure phase diagram and explain them in context of rheological measurements. We observe three distinct pattern morphologies: viscous fingering, dendritic fracturing, and system-wide fracturing, which correspond to the same packing fraction ranges as weak shear thickening, discontinuous shear thickening, and shear-jammed regimes.

Multiphase flows in deformable porous materials are important in numerous geological and geotechnical applications, however the complex flow behaviour make subsurface transport processes difficult to control or even characterise. Here we study gas-driven (pneumatic) fracturing of a wet unconsolidated granular packing confined in a Hele-Shaw cell, and present an in-depth analysis of both pore-scale phenomena and large-scale pattern formation. The process is governed by a complex interplay between pressure, capillary, frictional and viscous forces. At low gas injection rate, fractures grow in a stick-slip fashion and branch out to form a simply connected network. We observe the emergence of a characteristic length-scale-the separation distance between fracture branchescreating an apparent uniform spatial fracture density. We conclude that the well defined separation distance is the result of local compaction fronts surrounding fractures, keeping them apart. A scaling argument is presented that predicts fracture density as a function of granular friction, grain size, and capillary interactions. We study the influence of gas injection rate, and find that the system undergoes a fluidisation transition above a critical injection rate, resulting in directional growth of fractures, and a fracture density that increases with increasing rate. A dimensionless Fluidisation number F is defined as the ratio of viscous to frictional forces, and our experiments reveal a frictional regime for F < 1 characterized by stick-slip, rate independent growth, with a transition to a viscous regime (F > 1) characterized by continuous growth in several fracture branches simultaneously.

Using high-speed imaging and digital image correlation, we study the granular motion and deformation caused by pneumatic fracturing of a wet granular packing in a Hele-Shaw cell subject to a constant injection of air. These pneumatic fractures form patterns of conductive pathways whose form is determined by a complex interplay between pressure, capillary, frictional, and viscous forces. Saturated granular media is pneumatically fractured in this fashion in multiple natural, geo-engineering, and industrial processes. We outline the characteristics of these fracture networks and then examine individual fracture growth events and the local motion of grains with a time resolution of milliseconds. We observe intermittent frictional behaviour during these rapid fracturing events, describe an average velocity profile for the motion of grains during fracturing, and illustrate an average compaction profile as a result of these deformations.