Contact-scale insights into the shear stiffness of non-spherical granular materials

Small-strain shear stiffness (G0) is an essential parameter to predict deformation characteristics and dynamic properties of granular materials. It is empirically known that G0 increases with decreasing a void ratio (e0) and increasing isotropic stress level (p0′). Recently, the effect of particle shape on G0 has been studied; however, the mechanism underlying the evolution of G0 is not fully understood. Using the discrete-element method, this contribution quantifies the G0 of granular materials by performing small-strain probing where multi-sphere clumped particles are used to vary particle shape and surface topology systematically. The Hertzian contact theory is applied for each sphere-element contact to capture the stress-dependent contact stiffness. The results reveal that G0 is well correlated with e0 or mean coordination number for a given particle shape; however, G0 is measurably reduced when finer sphere-elements dominate inter-particle contact responses. The present study proposes two contact-scale expressions of G0 for non-spherical particles based on contact area and micromechanical effective medium theory (EMT) by extending the EMT expression for spherical particles; both can capture the effects of particle shape and p0′ on G0 under given conditions where particle breakage does not occur.