Impact of Three-Dimensional Sphericity and Roundness on Coordination Number

Abstract

Coordination number (CN) is a fundamental microscale variable in soils affecting the macroscale parameters of the material such as porosity, stiffness under loading, and stability under hydraulic gradients. However, most studies on CN have focused on sphere or ellipsoid packings using the discrete element method (DEM). By means of computed tomography (CT) and image-processing techniques, this work rigorously computes the three-dimensional (3D) sphericity and roundness of each grain in five sands and investigates the impact of particle shape on CN. The results show that the average coordination number (CNave) of different sands and the CN of grains within a given sand may be impacted differently by particle shape. For a given equivalent diameter of a given sand, more irregular grain packings show a subtle higher CN, and this change in CN increases with increasing grain size. However, air-pluviated irregular particle packings with poor gradation may exhibit lower average CNave because of particle orientational alignment, particle interlocking, and surface roughness.