The experimental contact behaviour of natural sands: normal and tangential loading

Abstract

A comprehensive series of tests was carried out using an innovative three-axis inter-particle loading apparatus, investigating the normal and shearing contact behaviour between sand particles of a variety of geological origins. The results show that the normal loading behaviour is very sensitive to the type of sand and its surface condition, and thus to its geological origin and history. For particles characterised by a highly regular shape and low surface roughness, such as those of a common quartz sand, good predictions may be made with models based on the elasticity theory, but at lower loads the particle roughness needs to be accounted for. In shearing the coefficient of inter-particle friction is highly variable, both for a single sand and between different sands, but the average values are controlled predominantly by the surface roughness. Current elasticity-based methods for predicting the tangential stiffness overestimate it considerably, but coaxiality between the forces and displacements indicates that the underlying assumption of elasticity with micro-slipping at the contacts may be correct.