Distinguishing between rheophysical regimes of fluid-saturated granular-flows using dilatancy and acoustic emission measurements

Abstract

Dry granular flows provide an ongoing challenge to physics and under saturation the multiphase physics is even more difficult to disentangle. A rich literature has elucidated the possible regimes achieved, however, the nonlinear nature of the multiphase process makes predicting the appropriate dynamic regime difficult. In this study, we introduce a new experimental strategy to identify the appropriate dynamical regimes by combining traditional methods with acoustic emission measurements. We sheared natural granular materials under dry, water and oil-saturated conditions while recording mechanical, acoustic and visual data. By applying alternate low and high velocity steps we respectively obtained quasi-static and inertial granular flow regimes. Dilation was observed for all high-velocity flows but its amount varied as did the degree of acoustic emission. At high velocities, the water-saturated flow dilated less and had reduced acoustic emissions relative to the dry case. In contrast, the oil-saturated flow dilated more while having even less acoustic emissions. This difference in trends of the dilation and acoustic emissions with increasing fluid viscosity suggests that oil and water granular flows achieved distinct dynamical regimes. Damping of granular pressure by reducing grain collisions and Dilatancy due to fully lubricated contacts are two competing processes influence the saturated shear physics and theoretically expected, but distinguishing between the regimes is difficult to anticipate. The acoustic emissions provide an extra piece of information that allows us to distinguish the physical regimes and determine the competition between processes that control the physics of saturated granular flows in the granular inertial regime.