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

The influence of particle shape on the shear modulus at very small strain (G_max) 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 (D_r) and mean effective stresses (p′). Additionally, computed tomography (CT) technique was employed to interpret the role of particle shape on G_max from a microstructural perspective. The test results reveal that under the same relative density condition, as the irregularity of particle shape increases, the G_max of the materials first increases and then decreases. Angular materials exhibit the lowest G_max values, primarily due to their larger void ratio, while the mediumly angular materials display the highest G_max values compared to rounded and angular materials. Additionally, it was observed that overall regularity (OR) can be used to describe the significant transitional G_max response of granular material in relation to the variations in particle morphology. As OR decreases, the sensitivity of G_max to p′ initially decreases and then increases, which was found to be related to the shape-dependent particle mean coordination number (\(\overline{Z}\)). Notably, in materials with an extremely low \(\overline{Z}\) value, G_max exhibits a significantly faster increase with p′. Consequently, based on test data from granular materials with a wide range of particle shapes and transitional G_max responses, practical equations for correlating the parameters of G_max prediction model with particle morphology were formulated and validated.