Novel observations for the impact of particle morphology on shear modulus of granular materials

Abstract

The influence of particle shape on the shear modulus at very small strain (Gmax) of granular materials remains poorly understood and correlated. Using both micro-CT and bender element tests, this study aims to further systematically investigate this influence by comparing six granular materials with distinct particle shapes. The study included materials with angular and rounded particles, as well as relatively spherical and moderately angular particles, with particle morphological factors assessed using micro-CT. A series of bender element tests was conducted on these materials under various relative densities (Dr) and mean effective stresses (p′). Additionally, computed tomography (CT) technique was employed to interpret the role of particle shape on Gmax from a microstructural perspective. The test results reveal that under the same relative density condition, as the irregularity of particle shape increases, the Gmax of the materials first increases and then decreases. Angular materials exhibit the lowest Gmax values, primarily due to their larger void ratio, while the mediumly angular materials display the highest Gmax values compared to rounded and angular materials. Additionally, it was observed that overall regularity (OR) can be used to describe the significant transitional Gmax response of granular material in relation to the variations in particle morphology. As OR decreases, the sensitivity of Gmax to p′ initially decreases and then increases, which was found to be related to the shape-dependent particle mean coordination number (Z̄). Notably, in materials with an extremely low Z̄ value, Gmax exhibits a significantly faster increase with p′. Consequently, based on test data from granular materials with a wide range of particle shapes and transitional Gmax responses, practical equations for correlating the parameters of Gmax prediction model with particle morphology were formulated and validated.