Multiscale numerical investigation into the effects of rock content and rock particle size on the macroscopic and mesoscopic mechanical characteristics of soil rock mixture

Soil-rock mixture is a typical two-phase composite material. The physicomechanical properties and relative quantities of each component greatly influence the macroscopic mechanical properties of the soil-rock mixture. This study takes the macroscopic and mesoscopic coupling perspective and uses the discrete element direct shear test as the main method to comprehensively investigate the effects of rock content and rock particle size on the mechanical properties of the soil-rock mixture. The results show that the macroscopic shear strength of soil-rock mixture specimens increases with the increase of rock content. The initial packing state and compactness of specimens affect their shear dilation performance to some extent. The contact force chain distributions within specimens under different soil-rock combinations differ significantly. However, a very obvious force chain band is observed in the specimens at the end of the shearing (ranging from the upper left of the shearing box to its lower right). The contact force branch vectors within the force chain band are thick and dense, with obvious directionality (all from top left to bottom right). Under the same vertical load, the average coordination number of particles on the shear surface decreases with the increase of rock content. Within the same specimen, the average coordination number of particles on the shear surface increases with the increase of vertical load.