Relationships between gradation and deformation behavior of dense granular materials: Role of high-order gradation characteristics

This paper numerically investigates deformation behavior of coarse-grained granular materials with emphasis on the effect of grain size distribution (GSD). Biaxial compression tests are simulated in two dimensions using distinct element method (DEM) on a set of samples composed of uncrushable spheres following a wide variety of GSDs. The results prove that high-order characteristics of gradation, such as the shape of the GSD curve, significantly affect deformation behavior of widely-graded materials. Two grading indices are proposed to consider the combined effects of the spread and the shape of the GSD curve, and they are highly correlated with the parameters of the materials' internal fabric. Strong correlations are found between the proposed grading indices and deformation parameters, such as those of the normal compression line and the critical state line (CSL) in the e-p space, and the deformation modulus. In contrast, using the more conventional coefficient of uniformity cannot reach effective gradation-dependent relations for those deformation parameters due to the deficiency in characterizing high-order features of gradation. This study suggests the need for incorporating high-order characteristics of gradation into a refined measure of size polydispersity in order to establish gradation-dependent relations of deformation parameters widely effective for polydisperse granular materials.