  Discrete element method simulations of confined bidisperse granular shear
flows elucidate the balance between diffusion and segregation that can lead to
either mixed or segregated states, depending on confining pressure. Results
indicate that the collisional diffusion is essentially independent of
overburden pressure. Because the rate of segregation diminishes with overburden
pressure, the tendency for particles to segregate weakens relative to the
re-mixing of particles due to collisional diffusion as the overburden pressure
increases. Using a continuum approach that includes a pressure dependent
segregation velocity and a pressure independent diffusion coefficient, the
interplay between diffusion and segregation is accurately predicted for both
size and density bidisperse mixtures over a wide range of flow conditions when
compared to simulation results. Additional simulations with initially
segregated conditions demonstrate that applying a high enough overburden
pressure can suppress segregation to the point that collisional diffusion mixes
the segregated particles.
