Shape effects in granular flow down a rough incline: Understanding the role of particle flatness and elongation

Dense granular flow on rough inclines provides a canonical setting for investigating gravity-driven mass movements, yet the role of particle shape remains insufficiently understood. Here we use discrete element method simulations to examine how particle flatness modifies inclined granular flow mobility and microscopic dynamics, and to compare these effects with those of particle elongation. Following Pouliquen’s framework, steady uniform flows are analyzed over a range of inclinations and layer thicknesses. The results show that flattening preserves the functional form of the flow rule but strongly modifies its parameters. The steady-flow scaling parameter β increases as particles depart from the spherical limit, indicating reduced flow mobility for flatter grains. The reduced mobility correlates with constrained particle rotation and orientational reorganization, with flattened particles progressively adopting a near-flat-lying configuration in the shear–normal plane. Comparison with elongated particles shows that flattening and elongation provide mechanically distinct routes away from spherical-grain behavior. Among the shape descriptors considered, sphericity ψ offers the most effective reduced representation of the steady-flow response: plotting β against ψ brings flattened- and elongated-particle data into closer agreement and reveals an empirical crossover in shape sensitivity near ψ ≈ 0.95 . These findings reveal the link between shape-induced changes in particle dynamics and reduced flow mobility, and provide a basis for shape-aware constitutive descriptions of dense non-spherical granular flows.