Segregation forces in dense granular flows: closing the gap between single intruders and mixtures

Using simulations and a virtual-spring-based approach, we measure the segregation force, Fseg, in size-bidisperse sphere mixtures over a range of concentrations, particle-size ratios and shear rates to develop a semiempirical model for Fseg that extends its applicability from the well-studied non-interacting intruders regime to finite-concentration mixtures where cooperative phenomena occur. The model predicts the concentration below which the single-intruder assumption applies and provides an accurate description of the pressure partitioning between species.