  Most previous experimental investigations of two-dimensional (2D) granular
column collapses have been conducted using three-dimensional (3D) granular
materials in narrow horizontal channels (i.e., quasi-2D condition). Our recent
research on 2D granular column collapses by using 2D granular materials (i.e.,
aluminum rods) has revealed results that differ markedly from those reported in
the literature. We assume a 2D column with an initial height of h0 and initial
width of d0, a defined as their ratio (a =h0/d0), a final height of h , and
maximum run-out distance of d . The experimental data suggest that for the low
a regime (a <0.65) the ratio of the final height to initial height is 1.
However, for the high a regime (a >0.65), the ratio of a to (d-d0)/d0, h0/h ,
or d/d0 is expressed by power-law relations. In particular, the following
power-function ratios (h0/h=1.42a^2/3 and d/d0=4.30a^0.72) are proposed for
every a >0.65. In contrast, the ratio (d-d0)/d0=3.25a^0.96 only holds for 0.65<
a< 1.5, whereas the ratio (d-d0)/d0=3.80a^0.73 holds for a>1.5. In addition,
the influence of ground contact surfaces (hard or soft beds) on the final
run-out distance and destruction zone of the granular column under true 2D
conditions is investigated.
