Micro-scale investigation of the role of finer grains in the behavior of bidisperse granular materials

Abstract

This paper presents a numerical study of the effect of fine content on the mechanical behavior of bidisperse granular materials using the discrete element method. Triaxial compression tests are performed on different samples with fine contents varied from 0 to 40%. It was found that, starting from 20%, fine content has a visible effect on the shear strength. The optimal fine content is about 30%, at which the shear strength is the best. An investigation into the granular micro-structure showed that the fine particles, on one hand, come into contact with coarse particles, but on the other hand, separate the latter ones as fine content increases beyond 20%. Thus, the part of the shear stress carried by the coarse–fine contacts increases, while the part carried by the coarse–coarse contacts decreases. For fine content ≤ 30%, the coarse–coarse contacts primarily carry the shear stress. Above this optimal fine content, the fine–coarse contacts overtake the coarse–coarse ones. The fine–fine contacts have little contribution to supporting the shear stress. For the studied range of fine content, the coarse particles primarily carry the shear stress, leaving the fine particles under relatively low stresses. Moreover, the matrix composed of fine particles is greatly softened by the shear loading. A classification of binary mixtures depending on their micro-structure was also proposed.