ABSTRACT
The flow of granular media has been the subject of numerous experimental and theoretical studies. However, until recently, the highly unsteady situation of a column of grains collapsing onto a horizontal plane due to gravity had not been investigated.Yet this situation is of particular interest for the geophysical issues of flow mobility and runout distance. Lately, several experimental works have brought new insights in the runout distance problem (Lube et al 2004a; Lajeunesse et al 2004; Balmforth & Kerswell 2004). The experiments consist of releasing suddenly an initially confined column of granular material, of initial height H0 and initial radius R0, and let it spread freely onto a horizontal plane. The main outcome of these studies consists of scaling laws relating the runout distance (R∞ − R0) to the initial geometry of the column both in quasi-2D (or planar) and axisymmetric configurations. When the initial aspect ratio of the column, a = H0/R0, is sufficiently large, the runout distance normalized by the initial radius of the column shows a power-law dependence on a. This power-law dependence is incompatible with a simple friction model, and suggests more complex dissipation mechanisms within the flow. However, no clear and comprehensive physical modeling of the collapse dynamics has been achieved yet.
