Failure mechanism of true 2D granular flows

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 dier markedly from those reported in the literature. We assume a 2D column with an initial height of h₀ and initial width
of d₀, a dened 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 (a0.65) 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.