Study on the packing and shear characteristics ofgranular mixtures via the DEM

Abstract

Granular mixtures are often encountered in civil engineering, but the micromechanical implications of their packing and shear characteristics are still unclear. In this study, the packing and shear characteristics of binary mixtures were studied using a three-dimensional discrete element method (DEM). The binary mixtures contained realistic gravel-shaped coarse particles and one of two tested fine particle shapes (namely, spherical or elongated particles). The densest isotropic samples were generated by using a frictionless condition. The initial void ratio and particle contacts of the packed samples were examined. This study shows that the particle shape of the fines affects the relationship between the initial void ratio and fines content (FC). The contact types in binary mixtures can be classified as coarse particle-coarse particle (CC contacts), coarse particle-fine particle (CF contacts) and fine particle-fine particle (FF contacts). A microscopic investigation of the particle contacts indicated that the coarse and fine particle shapes influenced the partial coordination numbers of the CC and CF contacts and the CF and FF contacts, respectively. All the samples were then subjected to numerical triaxial compression tests. The results show that the particle shape of the fines affected the magnitudes and evolutions of the peak (φp) and critical (φc) friction angles of the binary mixtures. Finally, an anisotropic analysis was performed to highlight the microscopic mechanisms that cause the shear strength to be dependent on the particle shape and FC.