DEM study on role of fines in mobility of dry granular flows considering particle size-shape correlation

Many field observations show that the shape characteristic of particles constituting natural or industrial loose deposits is often size-correlated, that is, either more regular or irregular for larger particles than fines, depending on the particle formation process. Motivated by this, the role of fines in mobility of gravity-driven dry granular flows has been explored numerically through the collapse of granular columns with fractal particle size distributions. A series of granular columns with different combinations of initial aspect ratio, fractal dimension and particle size-elongation correlation (i.e., positively, negatively correlated and uncorrelated cases) are prepared by the discrete element method to conduct column collapse simulations. Among which, a general framework for generating size-shape correlated particles has been proposed using the Fourier-based particle morphology characterization method. Results show that fines may enhance or hardly influence the mobility of dry granular flows, hinging on the actual particle size-shape correlation. Specifically, for the particle size-elongation uncorrelated and negatively correlated cases, the mobility of dry granular flows is almost independent of the fine content, while it increases with the fine content for the size-elongation positively correlated case. The underlying mechanisms are also explored to unravel the observed flow mobility differences from perspectives of the flow characteristic and energy dissipation.