The Effect of a Liquid Phase on Force Distribution During Deformation in a Granular System

Abstract

Two‐phase systems, where one phase is solid and the other is fluid, are widespread in nature. Examples include reservoir rocks holding vital fluids like water or petroleum, slurries of partially crystallized magmas, fluids migrating along faults filled with fault gouge, and even the semibrittle crust. Previous studies of two‐phase systems have shown that the fluid phase plays an important role in deformation localization and dynamics (e.g., Higashi & Sumita, 2009, https://doi.org/10.1029/2008JB005999; Reber et al., 2014, https://doi.org/10.1002/2014GL059832). Here, we present results from experiments investigating the influence of a fluid phase on force distribution in a granular media during simple shear. We use photoelastic polyurethane discs as the granular or solid phase and a linear viscous silicone as the fluid phase. The photoelastic property of the discs allows for direct observation and measurement of force magnitude and distribution. We compare the two‐phase experiments to granular experiments without silicone. The addition and percentage of the fluid phase has a strong impact on the force distribution and the overall force chain orientations. In the two‐phase system, the force chains form parallel to the shear plane and only rotate to the principal stress direction with an increase in strain. Locally, the fluid phase can support forces and terminate force chains over an extended period of time. Our results are in line with findings from numerical studies investigating the formation of slow slip events, proposing that these events are the result of dynamic interactions between solid and viscous phases.

Deformation of brittle clasts within a viscous matrix: Field and experimental observations

“…The resemblance between our semi-brittle experiments and viscous creep is not unexpected as previous studies show that the presence of a viscous interstitial fluid can redistribute stress rather effectively (Fusseis et al, 2006;Reber et al, 2014;Webber et al, 2018;Beall et al, 2019;Ladd and Reber, 2020). The dispersion of stress can occur by the viscous fluid transferring stress to surrounding force chains or by the formation of shear planes within the fluid itself.…”

“…Even in a system The brittle and viscous phases accommodate strain c) Supportive framework formed by the brittle phase that resembles a granular system. Adapted from Handy (1990) with a high brittle phase concentration, the rheological properties of the viscous phase, however, can still impact strain localization and deformation dynamics (Higashi and Sumita, 2009;Reber et al, 2014;Ladd and Reber, 2020).…”

The Impact of Matrix Rheology on Stress Concentration in Embedded Brittle Clasts

“…Semi‐frictional numerical experiments with constant viscosity matrix suggest that high viscosity contrasts between the matrix and the clasts can effectively lower the bulk shear stress required for clast failure (Beall et al., 2019a). In addition, analog experiments on elastic clasts embedded in a linear viscous matrix have shown that the matrix was able to sustain differential stresses over extended periods of time (Ladd & Reber, 2020).…”

“…For clast concentrations higher than 50% by volume, clasts can interact with each other and force chains or stress bridges can form (Beall et al., 2019a; Webber et al., 2018). In cases where the clast concentration is smaller, direct coupling between the viscous matrix material and the clasts, and matrix properties that can temporarily sustain differential stresses (Ladd & Reber, 2020) would be necessary to transfer stresses leading to the potential failure of clasts (Phillips et al., 2020).…”

“…Stress applied to such systems manifests itself in the formation of force chains, frictional sliding, and fracturing (Handy, 1990; Holyoke & Tullis, 2006; Johnson et al., 2004; Jordan, 1987; Li et al., 2007). However, even in systems with a high brittle phase concentration, the rheological properties of the viscous phase can still impact strain localization and deformation dynamics (Higashi & Sumita, 2009; Ladd & Reber, 2020; Reber et al., 2014). Experimental studies have revealed that the addition of a relatively small amount of viscous phase leads to increased localization and can dampen the frictional stick‐slip deformation signature (Higashi & Sumita, 2009; Reber et al., 2014).…”