Particle crushing in granular soils leads not only to gradation broadening but also to significant evolution in particle shape, particularly the progressive rounding of angular grains. While previous studies have shown that gradation broadening shifts the critical state line (CSL) downward in the mean stress–void ratio (p–e) plane without significantly affecting critical state shear strength, the role of shape evolution and its interaction with gradation has received less attention. This study explores the coupled variation of particle size and shape under crushing and its joint effect on the critical state behavior of granular soils. A series of drained (constant confining pressure) and undrained (constant volume) biaxial shear simulations was performed using a calibrated discrete element method model on reconstituted samples representing varying degrees of particle breakage. The results show that gradation broadening alone lowers the CSL in the p–e plane, but the shift becomes more pronounced when particle rounding is also considered. In the mean stress–shear stress (p–q) plane, gradation has little impact on the critical state shear strength, while shape change noticeably alters it. Similar combined effects of size and shape distributions are observed in the CSL representations in p—mean mechanical coordination number (Zm)—and p—contact normal anisotropy coefficient (ac)—planes. At the microscale, a particle’s mechanical role is governed not only by its own size and shape, but also by those of its neighboring particles. These findings highlight the importance of incorporating both gradation and shape variation to adequately characterize the evolving mechanical response of granular materials subjected to crushing.
Ali et al. (Wed,) studied this question.