Evolution of Meso-scale Structure at Critical State for Granular Media

Granular material is a typical multi-scale material, which physical and mechanical properties are similar to continuous medium in macroscopic scale, but discontinuous and strongly anisotropic in micro- and meso-scale. In this paper, numerical simulations of biaxial tests for ideal granular samples with different initial densities were carried out using discrete element method (DEM). Loop structures, which are represented by voronoi polygons, were taken as the basic meso-mechanical unit of granular material by mesh-subdivision. The evolutions of numbers, geometrical morphology for different loops were simulated and analyzed. From the mesoscopic point of view, critical state of granular media is the consequence of mutual transformation for higher-order loops and lower-order loops, the combined average and external manifestation of all loops.