The influence of particle size distribution on the stress distribution in granular materials

This study systematically explores the effect of the shape of the particle size distribution (PSD) on stress transmission in granular materials using three-dimensional discrete-element method simulations. Extending prior studies that have focused on bimodal mixtures of coarser and finer grains, a broad range of isotropically compressed specimens with spherical particles and linear, fractal and gap-graded particle size distributions is considered. Considering isotropic stress conditions, the nature of stress distribution was analysed by determining the mean effective particle stresses and considering the proportion of this stress transmitted by particles with different sizes. For gap-graded materials a contact-based perspective was adopted to consider the stress transmission both within and between the different size fractions. A clear correlation emerged between the cumulative distribution of particle sizes by volume and the cumulative distribution of particle sizes by mean effective stress for specimens with continuous PSDs. This correlation does not hold universally for gap-graded materials. In gap-graded materials the distribution of effective stress between the different size fractions depends upon the size ratio and the percentage of finer grains in the specimen. In contrast to specimens with continuous gradings, in gap-graded specimens the distribution of effective stress among the different size fractions exhibits a marked sensitivity to density. Basic network analysis is shown to provide a useful insight into effective stress transmission in bimodal gap-graded materials.