Experimental study on the compaction deformation evolution and energy dissipation characteristics of graded broken rock mass

Axial compression tests with lateral confinement conditions were conducted to investigate the deformation and energy dissipation of broken rock masses with varying Talbol gradation indices (n = 0.2-1.0) in a goaf's collapse zone, with real-time energy release monitored via acoustic emission (AE) technology. The compaction process occurs in three stages: initial, linear, and plastic consolidation. The void fraction decreases nonlinearly with stress, with a larger gradation index resulting in a higher initial void fraction but a smaller final reduction. After compaction, the fractal dimension of the samples increased significantly (ΔD = 0.1059-0.7946), narrowing the range from 2.0-2.8 to 2.7946-2.9059, demonstrating a homogenization effect. The evolution of AE energy is closely coupled to the compaction phases. The initial stage is dominated by low-energy, high-frequency signals, while later stages feature high-energy, low-frequency events from particle breakage. An increase in gradation index leads to a decrease in cumulative AE counts but a significant increase in the energy of individual events, revealing distinct energy release modes.