Investigation of compressibility of rockfill materials using DEM: Role of sample size and boundary condition

Understanding the in-situ behavior of rockfill materials through laboratory tests is challenging due to the influence of sample size. In this study, the discrete element method (DEM) is utilized to investigate the effects of sample size and boundary condition on the compressibility of rockfill materials at both macroscopic and microscopic scales. The results reveal that rockfill compressibility increases with sample size when rigid boundaries are applied, but no significant size effect is observed for periodic boundaries. Besides, the one-dimensional compression behavior of different initial packing varies with sample size under rigid boundaries, with the variance decreasing as size increases; however, this effect is negligible under periodic boundaries. Additionally, both the distribution uniformity of contact number and fabric anisotropy increase with increasing sample size under rigid boundary conditions. At a microscopic level, it can be observed that the sample size effect of granular materials is correlated to the coordination number per unit volume CN/(1 + e) for the considered particle shapes.