Avalanche dynamics on a rough inclined plane

Abstract

Avalanche behavior of gravitationally-forced granular layers on a rough inclined plane are investigated experimentally for different materials and for a variety of grain shapes ranging from spherical beads to highly anisotropic particles with dendritic shape. We measure the front velocity, area and the height of many avalanches and correlate the motion with the area and height. We also measure the avalanche profiles for several example cases. As the shape irregularity of the grains is increased, there is a dramatic qualitative change in avalanche properties. For rough non-spherical grains, avalanches are faster, bigger and overturning in the sense that individual particles have down-slope speeds up that exceed the front speed u f as compared with avalanches of spherical glass beads that are quantitatively slower, smaller and where particles always travel slower than the front speed. There is a linear increase of three quantities i) dimensionless avalanche height ii) ratio of particle to front speed and iii) the growth rate of avalanche speed with increasing avalanche size with increasing tan θr where θr is the bulk angle of repose, or with increasing βP , the slope of the depth averaged flow rule, where both θr and βP reflect the grain shape irregularity. These relations provide a tool for predicting important dynamical properties of avalanches as a function of grain shape irregularity. A relatively simple depth-averaged theoretical description captures some important elements of the avalanche motion, notably the existence of two regimes of this motion.

Rheological measurements of large particles in high shear rate flows

“…Moreover, aspherical particles demonstrate increased ordering near the walls (an effect which is more pronounced for the smooth walls). 33,34 The smooth wall experiments, however, show that when normalized by the size and shape dependent random loose packing fraction, / l , the relative apparent viscosity shows no dependence on the particle size or shape. Comparing the nylon to SAN particles, both have a high sphericity (w ¼ 1.00 and 0.98), but the nylon particles …”

Tailoring the frictional properties of granular media

“…With l/b ave = 1.17, the Cataphote grains show a slightly greater average asphericity than the large Mo-Sci grains, l/b ave = 1.12. It has been demonstrated that higher asphericity leads to a larger angle of repose 14 . Another reason for the discrepancy could be that the two larger types of grain also produce different packing densities, φ, whish would be a natural consequence of their aspherity 32 .…”

“…It has been shown experimentally that friction can also play an important role in granular segregation 9,10 , for example in the sharp transition from the reverse brazil-nut effect to the brazilnut effect 10 , but other work shows that this is not always the case 11 . The dynamical properties of avalanches were shown to depend on inter-particle friction, and two friction-dependent scenarios for granular avalanches on an incline were identified [12][13][14] .…”

Relation between self-organized criticality and grain aspect ratio in granular piles

“…[25] by simulation and in Ref. [16] by experiment. It was found that spherical grains have a lower angle of repose than nonspherical grains and that for nonspherical grains the angle of repose fluctuates much stronger.…”

“…Moreover it was shown that long thin rods are able to jam into a solidlike state [13], which can strongly influence the avalanche behavior in such systems. Front velocity, area, and height of avalanches on a rough inclined plane have been already investigated experimentally for different grain shapes [16].…”