Influence of fine particles on the stability of a humid granular pile

TL;DR

This study examines how small amounts of fine particles affect the stability of humid granular heaps, revealing that they can either fluidize or reinforce the heap depending on their concentration and environmental humidity.

Contribution

It provides experimental insights and models explaining the dual role of fine particles in granular heap stability, considering humidity effects.

Findings

Low fine particles fluidize the heap via granular lubrication.

High fine particles increase cohesion, leading to stick-slip instability.

Fluidification is humidity-independent, while stick-slip depends on humidity.

Abstract

We have investigated by rotating drum experiments the influence of a small amount of fine particles on the stability of a granular heap. The fine particles are shown to have a strong and ambivalent influence. For low fine particle content, the heap destabilizes by avalanches, and the fine particles tend to fluidize the heap. In contrast, for high fine particle content, they increase the cohesion of the heap, which destabilizes through stick-slip at the drum wall. We interpret and model the fluidification in the avalanching regime, which we show is independent of humidity, by granular lubrication considerations, whereas the stick-slip behavior, highly dependent on humidity, is understood by a solid friction model.