Strong Force Network of Granular Mixtures Under One-dimensional Compression

Abstract

We studied one dimensional compressive behaviour of gap-graded granular mixtures, using the numerical simulations of the three-dimensional Discrete Element Method (DEM). Spherical particles of different size ranges were generated inside a cubical box to numerically create granular samples with the particle size distributions of a sand-like material mixed with different proportions of a uniform silt-size material. The DEM samples were subjected to one-dimensional compression similar to the loading path of the oedometer test in soil mechanics. Micromechanical characteristics behind the compressibility of granular mixtures were investigated with an emphasis on the strong force network. Unlike monodisperse assemblies, the deviatoric stress is mainly attributed to contact forces with a magnitude greater than the mean contact force of the system, the deviatoric stress of these mixture materials is attributed to a combination of the different contact types between different particle sizes. There is a primary shear-strength related load-bearing contact network, and this depends on the relative proportion of the silt particles in the system. For systems with a very little amount of silt, mainly consisting of sand particles, the main contribution to deviatoric stress is due to the contacts between the sand particles. On the other hand, for systems that have the void space between sand particles efficiently occupied by silt particles, all contact types contribute to the deviatoric stress. If strong forces of a particulate system are those responsible for the deviatoric stress, the characteristic force - that separates strong and weak forces - depends on the contact-type, the particle size distribution and the stress level; the value of the overall characteristic force however is not far from the mean force value of the system.