Effect of relative humidity on the nonlinear elastic response of granular media

Abstract

We study the influence of relative humidity (RH) on the nonlinear elastic response of granular media. Previous work has shown that the nonlinear elastic response of consolidated granular media like rocks likely arises from two distinct mechanisms; however, we do not have a clear understanding of their physical origins at the microscopic scale. Here, we conduct dynamic acousto-elastic testing (DAET) on samples of glass beads under dry (∼10%), ambient (∼60%), and humid (∼100%) conditions at room temperature and a constant static stress of 4 MPa. DAET allows us to retrieve the full nonlinear elastic response, including transient softening and hysteretic effects. We find that the elastic nonlinearity of humid samples is an order of magnitude larger than dry samples. Moreover, we find that all extracted nonlinear parameters increase with RH. This overall increase in nonlinearity is consistent with findings from previous studies and with the hypothesis that water adsorption on the grains makes the contact junctions weaker and prone to greater disturbances when subjected to dynamic stressing. Our results also suggest that, if indeed both mechanisms coexist, they are affected in a similar fashion in these glass bead samples and cannot be distinguished by varying RH.

Effect of Grain Shape and Relative Humidity on the Nonlinear Elastic Properties of Granular Media

“…We prepare samples of spherical soda-lime glass beads (diameter 100-140µm, Mo-Sci Corporation, Rolla, Missouri) and angular, fine quartz sand (diameter 50-150µm, 99.8% SiO 2 with minor amounts of Fe 2 O 3 , Al 2 O 3 , <0.1% each, U.S. Silica Company) using a setup identical to our previous study (Gao et al, 2022). We place a 4.5 mm thick pack of granular media (i.e., glass beads or sand) on top of a steel block of area 10*10 cm 2 .…”

“…The sample is then quickly taken out of the sealed bag and a second steel block of identical size is placed on top of the granular layer. The sides are sealed using multiple layers of tape (Gao et al, 2022).…”

“…We then extract the magnitude of the harmonics 𝑅 where 𝑛 = 0, 1, 2. Using 𝑛 up to 2 is shown to be sufficient to capture the complexity of the nonlinear signatures (Gao et al, 2022).…”

“…To confirm this hypothesis and better understand the underlying physics, we seek to investigate the nonlinear elastic response of materials simpler than rocks, both in terms of composition and microstructural features. In our previous work (Gao et al, 2022), we studied the influence of relative humidity (RH) on the nonlinear elastic properties of glass bead samples. We found that all extracted nonlinear parameters increase with RH.…”

Resolving minute temporal seismic velocity changes induced by earthquake damage: The more stations, the merrier ?

“…The transient dynamics is generally interpreted as the result of 1) a phase of "damage" during deformation that arises from a variety of contacts (Ostrovsky et al 2019; which are broken at grain boundaries or at defect locations and 2) a phase of "healing" associated with thermally activated processes that bring the metastable contacts towards a new equilibrium state -a phase also called slow dynamics or relaxation (Guyer et al 1999;TenCate et al 2000). In rocks and near-surface geomaterials, this contact recovery is thought to happen due to micro-cracks and fracture closure (Meyer et al 2021) or re-arrangement of frictional shear zones (Lieou et al 2017) and with a large contribution of chemical processes modulated by moisture (Brantut 2015;Bittner & Popovics 2021;Gao et al 2022). Corresponding physical and phenomenological models can be developed from laboratory observations thanks to a fine control of the strain disturbance (Remillieux et al 2017), a well-resolved temporal acoustic monitoring system (that can observe relaxation timescales down to fractions of a second (Shokouhi et al 2017b)), simplified geometries (Yoritomo & Weaver 2020) or the knowledge of the physical properties of the chosen rock samples.…”