Mechanism of Sandpile Avalanche in Critical State

The dynamical characters of granular mixtures were investigated based on the concept of self-organized criticality (SOC). Through sandpile experiments with one-sided slope, it was discovered that a sandpile consisting of non-uniform sand with a sorting coefficientφ=2.85 exhibits SOC, while the large-scale avalanches of a sandpile composed of uniform sand with a sorting coefficientφ≈1 have a quasi-periodicity. It was believed that sandpiles have representative binary composition,i.e.a granular layer and a friction-resistance layer. The result indicates that in the critical state large-scale avalanches happen mainly in the granular layer for a non-uniform sandpile, whereas in both the granular and friction-resistance layers for a uniform sandpile. This shows that the dynamic characters of granular mixtures in the critical state are controlled by the non-uniform degree, and large-scale avalanches have two possible forms for sandpiles with different non-uniform degrees,i.e.,avalanche in the granular layer and avalanche in the granular and friction-resistance layers.