Abstract
Granular stockpiles are commonly observed in nature and industry, and their formation has been extensively investigated experimentally and mathematically in the literature. One of the striking features affecting properties of stockpiles are the internal patterns formed by the stratification and segregation processes. In this work, we conduct a numerical study based on DEM (discrete element method) model to study the influencing factors and triggering mechanisms of these two phenomena. With the use of a previously developed mixing index, the effects of parameters including size ratio, injection height and mass ratio are investigated. We found that it is a void-filling mechanism that differentiates the motions of particles with different sizes. This mechanism drives the large particles to flow over the pile surface and segregate at the pile bottom, while it also pushes small particles to fill the voids between large particles, giving rise to separate layers. Consequently, this difference in motion will result in the observed stratification and segregation phenomena.
Highlights
The pattern formation of particle stockpiles is primarily a practical concern
We present a numerical study of spontaneous segregation and stratification of binary spherical particles when forming a stockpile
Of the mechanisms dominating the pattern formation, we found that stratification is induced by the void-filling mechanism, while further pile avalanches and motion of large particles will result in segregation
Summary
The pattern formation of particle stockpiles is primarily a practical concern. During the stockpiling process, segregation and stratification happen spontaneously and directly lead to the de-mixing state of the particulate system. Williams [1,2,3], and Drahun and Bridgwater [4] experimentally studied the heap flow segregation using binary mixtures of spherical particles. They demonstrated a percolation mechanism where small particles tend to sink into the voids while large particles are able to float onto the surface and roll down to the pile bottom. Many researchers have reported this feature with the use of particles in different shapes. They further proposed several mechanisms to explain this phenomenon. Gray et al [8,9,10] experimentally
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