Scale separation between grain detachment and grain transport in granular media subjected to an internal flow

Based on a discrete element method, this paper investigates the basic mechanisms and the associated scales related to grain detachment and grain transport processes at stake in widely graded poly-disperse assemblies of spheres subjected to internal fluid flows. From the identification of force chains, particles sensitive to grain detachment are identified. Based on the computation of autocorrelation lengths, a typical length scale associated with this phenomenon is then defined. From the characterization of the void space as a pore network, particles eligible for grain transport are identified among the detachable particles. Based on the definition of a mean travel distance, the typical length scale associated with grain transport is finally characterized. The comparison between the two length scales highlights a scale separation between grain detachment and grain transport.