Kinematic Segregation of Flowing Grains in Sandpiles

TL;DR

This paper develops a theoretical model for granular segregation in sandpiles, capturing how large grains tend to settle at the bottom, aligning qualitatively with experimental observations.

Contribution

It introduces a coupled equations framework for surface flow segregation in granular mixtures, specifically modeling the kinematic sieving process in thick flow regimes.

Findings

Large grains segregate to the bottom of the pile

The model's predictions qualitatively match experimental results

Profiles of grain concentration are successfully calculated

Abstract

We study the segregation of granular mixtures in two-dimensional silos using a set of coupled equations for surface flows of grains. We study the thick flow regime, where the grains are segregated in the rolling phase. We incorporate this dynamical segregation process, called kinematic sieving, free-surface segregation or percolation, into the theoretical formalism and calculate the profiles of the rolling species and the concentration of grains in the bulk in the steady state. Our solution shows the segregation of the mixture with the large grains being found at the bottom of the pile in qualitative agreement with experiments.