Fluidisation, Segregation and Stress Propagation in Granular Materials

Abstract

The paper reviews recent experimental investigations into three areas of the dynamic and static behaviour of model granular materials. In the first, digital high speed photography and computer image processing are used to study the fluidisation of a two-dimensional model powder undergoing vertical vibration. The granular temperature is deduced from measured velocity distribution functions, and the scaling dependence on vibration frequency, amplitude and number of grains is compared with simulations and a simple analytical model. The system has also been used to investigate the size-ratio and acceleration dependence of particle size segregation behaviour for a single intruder in a two-dimensional bed of monodisperse particles at low accelerations. Particle trajectory maps show that, at all base accelerations, the intruder and surrounding particles move upwards at the same speed. Unlike recent suggestions in the literature, there appears to be no fundamental difference in segregation mechanism between the so-called intermittent and continuous regimes. The third area concerns the propagation of stress within a three-dimensional conical pile. A simple elasto-optical method has been used to measure the normal force distribution at the pile base. Experiments on sandpiles confirmed the existence of counter-intuitive pressure dips at the centre. Variations in surface roughness were found to have little effect on the pressure profiles.