Crucial role of sidewalls in granular surface flows: consequences for the rheology

In this paper we study the steady uniform flows that develop when granular material is released from a hopper oil top of a static pile in a channel. More specifically, we focus oil the role of sidewalls by carrying out experiments in set-up of different widths, from narrow channels 20 particle diameters wide to channels 600 particle diameters wide. Results show that steady flows on pile are entirely controlled by sidewall effects. A theoretical model, taking into account the wall friction and based oil a simple local constitutive law recently proposed For other granular flow Configurations, gives predictions in quantitative agreement with the measurements. Tills result gives new insights into Our understanding of free-surface granular flows and strongly supports the relevance of the constitutive law proposed.