FORCE DISTRIBUTION IN A TWO-PHASE MEDIUM DURING SIMPLE SHEAR

Two phase systems where a solid phase and a liquid phase coexist are common in nature and are of societal and economical importance. Such systems include reservoir rocks filled with hydrocarbons, partially crystallized slurries of magma, water saturated landslide material, and mid-crustal rocks where different mineral phases are either viscous or brittle. Here we investigate the impact of a fluid phase on the stress distribution in a mixed granular-viscous system. We use a granular photoelastic material with a viscous silicone as fluid phase filling the spaces between the discs. In a purely granular material force chains, frameworks of highly stressed grains surrounded by unstressed grains, form during deformation, while in a fluid system the deformation is non-localized. We perform experiments on a spring pulled simple shear table with energy conserving boundary conditions. We record force and displacement during shear. The photoelastic quality of the granular material allows us to see internal stresses due to patterns of constructive and destructive interference as light passes through the material. From those patterns we deduce the amount of stress each individual disc is experiencing. Our experiments show that the liquid phase is able to contribute significantly to the force distribution in the system leaving force chains weaker and not connected. Understanding force distribution in a two-phase system is crucial for efficient extraction of hydrocarbons, assessing risks correlated to long runout landslides and initiation of earthquakes in the middle crust.