Physical elucidation of the behaviors of sand-pile avalanches like self-organized criticality and like characteristic earthquakes

点击翻译按钮获取中文摘要

It is known that the behavior of avalanches in sandpile experiments is categorized into two types; one is the self-organized criticality like behavior, and another is the characteristic earthquake like behavior. These two types are determined solely by the ratio of sand diameter to the diameter of the disk on which the sandpile is created. This fact has been confirmed by a number of experiments, but the satisfactory physical explanation has not been given. The purpose of this study is to clarify the underlying physics of this phenomenon. We focus on the stress chain structure inside a sandpile. So we use a photo-elastic analysis of two-dimensional sandpile made of photo-elastic material and a simulation by discrete element method(DEM).A detailed observation of the results of the experiment and the simulation suggests a possible mechanism of avalanches: for a sandpile in a critical state, what determines the size of avalanches may be some kind of inhomogeneity.When the pile is small, the size of avalanches is small because the uneven distribution of particles on the surface may be the dominant inhomogeneity of the system. When the pile becomes large, however, the deep inside of the pile is tightened and consolidated while the part near the surface is never tightened because of the repeated avalanches. The contrast in strength becomes the main factor of the inhomogeneity.