In this work, a digital imaging technique is used to study the superficial fluctuations observed when a granular packing is slowly driven to the threshold of instability. The experimental results show the presence of three types of events. Small superficial rearrangements of grains are observed during all the experiments. They present a power-law behavior although the system is not in a critical state as predicted by self-organized criticality models. In thick granular piles, large rearrangements are detected at regular angular intervals. They are related to the threshold of instability of the contact network that relaxes to stable configurations producing internal rearrangements of the grains. Finally, an avalanche is triggered when the superficial beads that are set in motion acquire enough momentum to destabilize grains from layers below.

A packing of equal glass beads is placed on a box with a rough bottom. The box is slowly inclined till an avalanche begins at a critical angle. The avalanche dynamics decreases the surface slope until a second critical angle is reached. In previous works [1–3], the stability of the packing was found to be affected by the number of layers, the packing length and the surrounding humidity.

We report here an experimental study on surface granular flows. The granular packing is made of monosize glass beads initially poured in a box with controlled humidity. We have first studied the angles before and after the avalanche, and the mass displaced out of the box during the avalanche as a function of the number of layers of the packing. For small packings, up to approximately 10 layers, the stability of the system is significantly affected by the bottom rough surface. On the contrary, for thicker systems, the critical angles are unchanged with variations of the number of layers. In a second experiment, in the same apparatus in 3d and also in 2d, we have studied flow of a mass of grain on a surface near the situation where no accretion nor erosion exist (at the neutral angle). The influence of the geometry of the system is investigated.

We report both an experiment and numerical simulations on superficial fluctuations of a slowly driven granular system: a box filled with a certain number of layers of glass beads is tilted very slowly up to the maximum angle of stability where an avalanche is produced. The avalanche decreases the slope of the free surface of the packing until a second critical angle is reached: the angle of repose. During the build up period many rearrangements occur on the free surface. The distribution function for the observed mass fluctuations follows a power-law behavior. We reproduce this results (rearrangements and avalanche) with a cellular automata model which takes into account the transfer of momentum to layers below. It is the purpose of this work to study the transition between static and flowing states in a very slowly driven granular system. We will focus on the very reach behavior of the surface rearrangements leading up to a large slide.

The influence of the granular packing length on the avalanche parameters, such as its mass and the critical angles at which it begins and stops, is studied for packings of mono size glass beads under a controlled humidity environment.In order to understand the dynamics of this kind of systems, experiments are performed in boxes of two different dimensions to see the influence on the parameters. For both boxes, the critical angles show the same qualitative behavior. While the number of layers involved in the avalanche are determined by the box dimensions.

We report an experiment on a granular packing: a box filled with glass beads is tilted very slowly up to the maximum angle of stability where a big avalanche is produced. During the build-up period many rearrangements occur on the free surface of the packing. Digital imaging was used to study these rearrangements. The probability distribution of sizes for the observed mass fluctuations follow a power-law behavior, which is the signature of self-organized criticality. However, this description breaks down in the limit of big rearrangements where inertia effects are not negligible.

This paper reports an experimental study on avalanches in a granular material contained in a confined geometry. The granular packing is made of monosize glass beads initially poured into a box that is slowly inclined until an avalanche takes place at a critical angle straight theta(M) (maximum angle of stability). The avalanche involves a decrease of the surface slope until a second critical angle straight theta(r) (angle of repose) is reached. Both angles and the mass displaced out of the box during the avalanche are studied as a function of the height of the granular packing. In order to avoid cohesion effects, experiments are carried out in a humidity controlled environment. For small packings, up to approximately ten layers, the stability of the system is significantly affected by the rough surface at the bottom. In contrast, for thicker systems, critical angles do not depend on the height.