The use of weathered phyllite waste slags generated from the excavation of cuttings and tunnels as roadbed filler material can effectively address issues related to filler scarcity, environmental protection, and cost. This study focused on weathered phyllite obtained from a highway expansion project in the Longnan Area of Gansu Province, China. Various experiments were conducted in a laboratory setting, including compaction, unconfined compressive strength (UCS), California bearing ratio (CBR), permeability, and disintegration tests, to investigate the response of mixtures with different gravel contents (GCs), ranging between 30 %-70 % by weight of weathered phyllite filler (WPF). The test results indicate the presence of a critical GC threshold. At 55 % GC, the WPF exhibits optimal compaction, the highest UCS and CBR values, and the lowest permeability and disintegration rates. Upon reaching this critical GC threshold, the phyllite gravels contact each other to form a skeletal structure, while fine grains fill the gaps within this structure to create a denser skeleton configuration. Coarse phyllite gravels are more prone to fragmentation into finer grains, which can effectively occupy large, medium, and small voids between particles. Consequently, the WPF exhibits enhanced structural density and improved mechanical and hydraulic properties. These findings provide a theoretical reference for the engineering application of phyllite in mountainous projects.

The particle crushing effect of coarse-grained soil has been widely studied. This study conducted lateral compression tests under high-pressure conditions to study the compression characteristics and particle crushing laws of waste particles from tunnel excavation of phyllite. Samples with continuous and intermittent gradation were set up to analyze the physical parameters such as compression deformation law, gradation curve, crushing index, and plastic work before and after loading. The results show that the strain of each group of samples increases rapidly with stress during the loading process and then gradually stabilizes. The continuous group gradation shows good compressive bearing capacity. As the content of phyllite particles decreases, the overall deformation of the samples can be effectively reduced. Under high stress, the grading of each intermittent grading sample gradually converges to a continuous grading, with similar physical and mechanical properties. The fragmentation indicators applicable to the particles of waste rock in phyllite are Br and Bg. Establishing a hyperbolic model to fit the plastic work and relative fragmentation rate Br during the compression process, it was found that fitting the plastic work model can better characterize the fragmentation law of waste particles in phyllite. The research results can provide certain reference and guidance for further understanding the compression characteristics and particle fragmentation laws of soft rock waste materials such as phyllite, as well as for the filling of geotechnical engineering structures.