From Sedimentation to Suspension: Critical Strain as a Predictor of Particle Resuspension Thresholds

Abstract

Viscous resuspension, the process by which sedimented particles are re-entrained into a fluid under flow, is central to numerous natural and industrial systems, including environmental contaminant transport, riverbed erosion, and biogeochemical cycling. Despite its ubiquity and importance, predicting when and how resuspension occurs remains challenging, particularly under oscillatory shear, where particle interactions are nonlinear, collective, and time-dependent. Here, we examine the resuspension dynamics of dense, non-Brownian suspensions under both steady and oscillatory shear using bulk rheometry and in situ rheo-microscopy over a broad range of particle volume fractions ({\phi}= 0.30 to 0.55). We demonstrate that strain is the key control parameter governing the transition from a sedimented bed to a fully suspended state. This strain-driven onset is mediated by effective interparticle collisions and collective particle motion. We develop a predictive model that captures the observed strain thresholds as a function of volume fraction, allowing for the construction of a new state diagram delineating sedimentation, resuspension, and full suspension regimes. These findings reveal a robust, strain-controlled resuspension mechanism and establish a unified framework for predicting suspension behavior across steady and oscillatory flows, offering new tools for managing particle-laden transport in geophysical, biological, and industrial environments.