Flow of different material mixtures in a rotating drum

Debris flows can be considered as mixtures of coarse particles dispersed in a viscous matrix, composed of fine sediment and water. Experiments in a rotating drum with a diameter of 2.5m have been carried out to study the flow behaviour of different material mixtures, ranging from granular avalanches to viscous fluids and grain – fluid mixtures of varying sediment concentration and matrix viscosity. The bulk shear stress at the channel boundary was measured for the different mixtures. The macroscopic flow behaviour is described on the basis of the evolution of flow resistance with increasing flow velocity, and is used as a criterion to differentiate between the frictional, viscous, and collisional flow regime. Our results are only in partial agreement with a classification of flow regimes based on threshold values of dimensionless Bagnold and Savage number found in literature.