Influence of Friction and Particle Morphology on Triaxial Shearing of Granular Materials

Abstract

The present paper addresses the influence of shape, size, and frictional characteristics of granular materials by utilizing X-ray computed tomography (CT) imaging and FEM. High-fidelity triaxial shearing simulations are conducted on a realistic assembly of sand grains. Applicable boundary conditions are represented, including the latex membrane for applying confining pressure. For this research, two poorly graded clean sands (SP) with distinct grain morphologies of round and angular particle shapes are considered. The effect of the particle size is naturally embedded in two materials with a difference of small size fraction grains present in angular sand. The deviatoric stress and volume change response increase up to the value of friction coefficient (μ) equal to 0.5 for rounded sand, and the strength-deformation response is unaffected by a further increase in friction. The axial strain, corresponding to peak deviatoric stress, did not depend on the friction value for identical initial microstructure and boundary conditions. The microscale investigation suggests a similar mean coordination number and percentage of grains with a coordination number less than two for friction values producing similar responses. The angular sand resulted in higher strength and low dilation compared to the rounded sand for friction value that best reproduces experimental results. The strength increase due to the particle shape effect becomes less pronounced for smooth grains. The grain-scale analysis indicates angular sand exhibits less dilation in contrast to the general observation in the literature due to smaller grain fractions absent in rounded sand, highlighting the need to introduce additional subclassifiers in classifying SP sands. The localized deformation pattern remains unchanged with friction and varies with grain shape. An attempt is made to link micromechanical insights to the macroscale response.