Influence of Sand Morphology on Interparticle Force and Stress Transmission Using Three-Dimensional Discrete- and Finite-Element Methods

Abstract

In the last two decades, particle morphology has emerged as an essential and critical property for proper evaluation of the constitutive behavior of granular materials. When a mass of sand is loaded in a confined compression, a complex network of force chains develops and evolves to resist the applied stresses. Force chains have been extensively studied in the literature using the discrete element method (DEM) and to a lesser extent using the finite-element method (FEM). This paper investigates the influence of three-dimensional (3D) sand morphology on the onset and evolution of force chains within sand using both 3D DEM and FEM simulations. In-situ synchrotron microcomputed tomography (SMT) technique was utilized to acquire multiple 3D scans of a specimen composed of natural silica sand that was loaded under one-dimensional (1D) confined uniaxial compression. The SMT scans were processed and used to calibrate parameters for both DEM and FEM models, where particle sizes and shapes closely matched the natural morphology and fabric of sand particles within the tested specimen. In another virtual specimen, individual sand particles were substituted with equivalent spherical particles that have the same volume and center of mass. FEM and DEM simulations were then executed on the virtual specimen using the same model parameters that were calibrated by the tested sand specimen. A comparison between the numerically simulated results of the virtual and tested specimens revealed a stiffer boundary response of reaction load versus displacement at the top loading platen of the specimen composed of particles with sand-like morphology. On the contrary, a microscale assessment showed higher particle stresses and interparticle contact forces between the spherical particles than the sand-like particles under the same boundary load on the top-loading platen. The results of the paper advocate for the importance of modeling sand using the actual sand morphology in a quest for an accurate numerical prediction of interparticle contact forces, particle stresses, and the development of force chains in sands.