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 ( 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 ( $$\overline{Z}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mover> <mml:mi>Z</mml:mi> <mml:mo>¯</mml:mo> </mml:mover> </mml:math> ). Notably, in materials with an extremely low $$\overline{Z}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mover> <mml:mi>Z</mml:mi> <mml:mo>¯</mml:mo> </mml:mover> </mml:math> 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.