Correlation between grain shape and critical state characteristics of uniformly graded sands: A 3D DEM study

The multi-scale characteristics of particle morphology, including the overall form, local roundness and surface roughness, affect the critical state behavior of sands and should be considered in modern critical state-based continuum constitutive modeling. Despite extensive experimental and numerical studies, no consensus has been reached as to how particle morphology may quantitatively dictate the critical state response of sands. This study presents a numerical investigation based on discrete element method (DEM) in an attempt to address this outstanding issue. Five DEM samples of uniformly graded sands consisting of realistic shape clumps and ideal spheres of different mass proportions are prepared and subjected to conventional drained and undrained triaxial compression under different initial void ratios and stress states. A 3D overall regularity ( OR ) index is adopted to quantify both the overall form and local roundness characteristics of these assemblies. It is shown that this shape parameter OR may effectively help to elucidate the correlation between mechanical properties, especially the critical state behavior of sand and particle shape, and has a great potential for incorporation into the framework of anisotropic critical state theory for constitutive modeling of sand behavior. The study helps to advance our cross-scale understanding of microscopic grain-scale morphology information in relation to macroscopic soil behavior.