Stress Distribution Of Cohesionless Granular Pile

Granular media have been the focus of intense interest among physicists in the last few years not only because their obvious practical and engineering importance but also the basal research importance. Being a kind of condensed state system, they represent both solid-like and liquid-like features. Their fundamentality characters have not been explained distinctly so far. A classical paradigm is the press distribution in the cohesionless granular pile arisen by its gravity. Experiments reported that the maximum of the stress profiles under static granular pile is not at the center like we think instinctively but beside the center. Namely, there is a dip in it. In order to explain the puzzling phenomena, a number of inventive approaches have been taken. Some seek to account for the dip by viewing the pile as a stack of "wigwams," along whose sloping sides but vertical the press propagates. Others have shown that the central dip is compatible with the conventional continuum mechanics, in which the pile is viewed as a central elastic zone flanked by an outer plastic zone in which the stress is at the Coulomb condition limit. A third group has argued that granular material requires a new constitutive law and it is involved in the history of building the granular pile.In this article, we shall introduce some physical characteristic of the granular media and make a farther research investigation about the stress dip. We consider that under the situation of single granule is much smaller than the granular pile, the system can be looked as continuum media and it's stress be deal with theory of elasticity. Supposing removing the gravity is of converse, elastic and without any plastic distortion and dissipation, elastic theory still suit the static granular pile. Only because the density of the pile is variational greatly, its elasticity coefficient varies with the asymmetrical density. The computation using the model built with this theory shows that there is a "central dip" in the press distribution at the base of the pile, if the center is in low density but the sides in high. So we suggest: for the conical (or wedge-shaped) piles formed by pouring slowly grains from a point (or a line), the dip may have relation to the small density variation. And the variation may be due to the phenomenon that the pile is slightly tapped by the down-rolling grains along the pile surfaces.