Transition to movement in granular chute flows

This experimental investigation deals with the observation of the behaviour that dense granular materials present when they flow in steady regime on a rough chute, focusing the attention on the transition to movement of the b ed and on quantities involved as the internal friction angle. An important aspect of the study is the identification of parameters that distinguish gr anular from fluid flows, aiming to verify the possibility to describe a gra nular bed as it was a pseudo-fluid having a particular theological behaviou r. In the experiments we have not used idealised particles (spheres, rods o r disks) but sieved powders of ethylenediaminetetraacetic acid (EDTA), cons tituted of non-spherical particles with polydisperse size distribution and surface roughness. A static and a flowing (dynamic) layer are clearly ident ified. The thickness of the observed layers (static and dynamic) along the chute has been measured for different inclination, finding out that they co llapse into a single curve when considered in non-dimensional scale. On the ground of the experimental data we propose a direct way of measuring the d ynamic friction angle from chute observations and a simple constitutive law for granular materials in the frictional regime of motion. The law has bee n tested using velocity profiles obtained by filming the flowing granular b ed. (C) 2001 Elsevier Science Ltd. All rights reserved.