Characteristics of void distribution in caving zone and their impact on gangue slurry diffusion properties

High gangue emission has emerged as a significant issue impacting the ecological environment in mining areas. Utilizing gangue as an aggregate material to prepare gangue slurry for filling caving zones has gained popularity as a solution. However, due to the intricate nature of coal mine caving zones, the diffusion mechanism of gangue slurry is highly complex, necessitating the elucidation of its diffusion laws to effectively guide mine-filling practices. In this paper, we conducted an analysis of the impact of lithology, skeleton particle gradation, and axial stress on the distribution characteristics of the caving zone, leveraging the internal void evolution test system of mining rock mass and the simulation approach for skeleton particles of fractured rock mass. Furthermore, we established a fluid force balance model to investigate the diffusion characteristics of gangue slurry within the void. As the lithology hardens, the coarse particle size within the skeleton particle grading increases. Consequently, the void rate within the caving zone gradually expands, the void fractal dimension becomes increasingly prominent, and the diffusion depth of gangue slurry gradually intensifies. Lithology serves as the primary factor influencing gangue slurry diffusion. When the lithology hardens, the void ratio increases by 0.26, the void fractal dimension rises to 0.13, and the gangue slurry diffusion depth expands by 208 meters. An industrial practice of gangue grouting has been implemented. The results of on-site monitoring indicate that the diffusion range of gangue slurry aligns with the aforementioned findings, thereby effectively addressing the challenges associated with gangue disposal.