Synergistic effects of particle shape and size distributions on the maximum shear modulus of granular materials: A DEM-based investigation

The maximum shear modulus ( G ₘₐₓ) is a crucial mechanical property of soils. However, the influence of particle shape on the G ₘₐₓ is not yet fully understood, particularly in granular systems comprising a mix of different particle shapes. This study comprehensively investigates the joint influence of particle shape distribution and particle size distribution on the G ₘₐₓ of granular soils through discrete element method (DEM) simulations. Two series of simulations were conducted: the first series examined the effect of particle shape and fines content ( FC ) under a fixed coarse-fine particle size ratio ( R d ), while the second series analyzed the influence of particle shape distribution and R d with a fixed FC of 20 %. The results of Series 1 indicate that, for granular system composed of particles with a certain shape, increasing particle irregularity increases G ₘₐₓ whereas increasing FC decreases G ₘₐₓ. The mechanical void ratio ( e ₘ) correlates strongly with G ₘₐₓ across different FC levels. However, particle-shape effects on the G max are not fully captured by e m , as the proportion of rattlers decreases with increasing particle irregularity. The results of Series 2 indicate that spherical small particles exert a stronger lubricating effect between large particles compared to irregular small particles. Overall, specimens with irregular large and irregular small particles, as well as specimens with irregular large and spherical small particles, exhibit higher G ₘₐₓ values than specimens with spherical large and spherical small particles, or specimens with spherical large and irregular small particles. However, this trend may exhibit variations depending on R d and particle shape. These variations can be attributed to the distinct contributions of contact types (i.e., coarse-coarse, coarse-fine, and fine-fine) in terms of both their number and the force transmission characteristics across various particle shape distribution configurations. Finally, we introduce a modified void ratio that accounts for both unstable and inactive particles, thereby quantitatively normalizing the effects of particle size and shape distributions on the G ₘₐₓ. • Synergistic effects of particle shape and size distributions on G max were investigated. • Microscopic mechanism of the joint influence on G max was clarified through DEM. • Distinct roles of particles with varying shapes, classified as large or small, were elucidated. • A modified void ratio was proposed, offering superior predictive performance for G max .