Macro-micro scale investigation of gradation area effects on particle breakage characteristics of coarse-grained soils

Particle breakage is a significant cause of deformation and strength degradation in coarse-grained soils. Under the influence of gradation, the characteristics of particle breakage become more complex, posing challenges to the safe design of coarse-grained soil engineering. Previous studies have shown that when the particle size range remains unchanged, the gradation area S can fully represent the gradation changes of the soil. To explore the macroscopic and microscopic effects of the gradation area S on particle breakage, this paper conducts triaxial tests on coarse-grained soils with different gradation areas S , and uses discrete element technology to construct a numerical model to systematically study the macroscopic laws and microscopic mechanisms of particle breakage caused by gradation. The results show that when the confining pressure remains constant, the particle breakage index B r decreases with the increase of the gradation area S , and the two show a linear relationship, with the coefficient of determination exceeding 0.9. Based on the test results, a B r calculation formula considering the influence of the gradation area S is proposed, and the reliability of the formula is verified by combining existing results. The gradation area S significantly changes the microscopic mechanical response by affecting the proportion of coarse particles, and thereby affects the degree of particle breakage. Specifically, as S decreases and the proportion of coarse particles increases, the irregularity of particle motion is significantly enhanced, the proportion of strong chains increases, and the number of tensile fractures increases. The synergistic effect of these microscopic mechanisms is the intrinsic reason for the higher degree of particle breakage in soils with a lower gradation area S . The research results provide theoretical support for the stability design and risk prevention of coarse-grained soil engineering.