Ambivalent role of fine particles on the stability of a humid granular pile in a rotating drum

•The influence of fine particles on the stability of a humid granular pile was studied.•At low fine content, the pile destabilizes through avalanches.•At higher fine content, the pile destabilizes through stick–slip at the drum wall.•The dust fluidizes the pile by granular lubrication in the avalanching regime.•The dust solidifies the pile by jamming in the stick–slip regime.

We have studied the influence of fine particles on the stability of a granular medium in a rotating drum. The stability diagram of this system was established as a function of the drum rotation speed, fine particle content and relative humidity. Four regimes were observed. At low fine content, an avalanching regime is encountered at low rotation rate, and a continuous flow regime at high rotation rate. At high fine content, a stick–slip regime at the drum wall is seen at low rotation rate and a continuous sliding regime at high rotation rate. The influence of fines is ambivalent. At low fine content, they fluidize the pile and decrease its stability, by granular lubrication. At high fine content, they solidify the pile and increase its stability, by jamming the grain assembly. The enhancement of humidity increases the stability for high fine content, but has no effect for low fine content.

Graphical abstractWe have studied the influence of dust on the stability of a humid granular pile in a rotating drum. This influence is both huge and ambivalent, the dust is either fluidizing the heap by granular lubrication (at low content), or solidifying it by jamming (at higher content).Figure optionsDownload full-size imageDownload as PowerPoint slide