Abstract

In this paper the effects of size-segregation on flow's mobility and final morphology of axisymmetric collapses of dry, cohesionless, natural polydisperse grains, were experimentally investigated. Particular attention was paid to effects of initial particle organization of grains on runout properties. Several experiments were conducted on vertical columns of inner radius r(i) and height h(i), finding a key role of aspect ratio a = h(i) /r(i) on the structure of the dimensionless curves r* = (r(f) - r(i))/r (i) and h* = h(f) /h(i) vs a. These curves can be characterized by power-law fitting functions, where r(f), h(f) are the final radius and height of deposits. The fitting parameters of these functions show two mobility regimes, but with significant departure from some results reported in literature. These differences emphasize the need of considering the effects of initial arrangement of grains into the column and the non-uniformity of grain-size distribution on these scaling curves. Measurements of the final profiles h(r) are also reported obtaining a persistent " Mexican-hat" shape, although showing a difficulty for defining an universal scaling curve for this data. Coincidentally, the dimensionless energy dissipation parameter ( epsilon (a)) follows a similar trend as that reported for uniform grains, suggesting that both polydisperse and uniform granular materials dissipate energy almost in the same way.