Laboratory Investigation of Breakage and Deformation Characteristics of Phyllite Residual Fills under Varying Gradation Conditions

To elucidate the coupled breakage–deformation mechanisms of soft rock residuals in large-scale embankment applications, this study focuses on phyllite materials from the Kangluo Expressway project in Gansu Province, China. A combined experimental and numerical investigation was conducted under varying gradation conditions to examine interactions between particle breakage and deformation. Talbot continuous gradation curves (n = 0.30, 0.50, 0.7) and corresponding single-sized gradations were evaluated. A total of 400 single-particle crushing tests were performed to derive the Weibull modulus m and characteristic strength σ₀​ through statistical fitting. One-dimensional confined compression tests were then conducted in a steel cylinder (150 mm diameter, 300 mm height) under axial stresses from 0 to 15 MPa to quantify the breakage ratio. In the numerical analysis, a Fragment Replacement Method (FRM) was implemented within the PFC3D discrete element framework. When the octahedral shear stress exceeded a fracture threshold, the mother particle was replaced by 14 Apollonian sub-particles, with conservation of mass and momentum strictly enforced. The simulation results aligned closely with experimental data regarding stress–strain behavior and the correlation between Talbot gradation and breakage ratio. These findings provide experimental validation and theoretical guidance for utilizing soft rock waste and calibrating discrete element models.