Experimental Study on the Effect of Realistic Shapes on Single-Grain Crushing Characteristics of Fragmented Weathered Phyllite as Subgrade Filler

Grain morphology—a fundamental characteristic of granular materials—significantly influences their macroscopic behavior. This study comprehensively investigates the effect of crushing strength distribution, crushing mode, force–displacement curve, size, and realistic shape characteristics on the crushing behavior of weathered phyllite grains. A series of single-particle crushing tests was conducted to examine the Weibull distribution and crushing strength of weathered phyllite grains; three representative grain morphologies were considered: general form, local roundness, and surface roughness. Realistic shape characteristic parameters before and after particle crushing were obtained using three-dimensional scanning and image processing techniques. The results demonstrate that the particle crushing strength distribution of weathered phyllite grains can be accurately described using a Weibull function. The Weibull modulus, characteristic strength, and crushing strength of the weathered phyllite grains decreased with increasing grain size. Moreover, the three fragmentation modes—fracturing, splitting, and chipping—corresponded to the force–displacement curves displaying single-peak, double-peak, and multipeak characteristics, respectively. Furthermore, flatter and more slender grains exhibited more prominent angular characteristics. While smoother grain surfaces were more susceptible to fracture failures, rougher surfaces were less prone to such failures. These findings demonstrate the pronounced size effect observed in weathered phyllite grains. Furthermore, compared to the original weathered phyllite grains, an increase in fineness, angularity, and surface roughness, along with a decrease in flatness, was observed in the subparticles resulting from crushing. These findings provide a theoretical reference for the engineering application of weathered phyllite as roadbed filler material in mountainous projects and deeper insights into the effect of morphological features on grain crushing behaviors.