Study on Fractal Characteristics of Compaction Deformation and Recrushing of Graded Crushed Rock Masses under Compression

The characteristics of compaction deformation and refracturing in crushed rock mass within collapse zones are significant for managing overburden movement and preventing ground subsidence. To explore the compression characteristics and crushed evolution of crushed rock mass, this study used a compression testing system for crushed rock mass to conduct experiments under different axial stresses and gradation indexes. The influence of these factors on the axial displacement, porosity, mass fraction, and relative crushing index of the crushed rock mass was determined. A model was established for the deformation and crushed characteristic parameters under stress, and the limiting values of axial displacement, fractal dimension, relative crushing index, and porosity of crushed rock mass under different gradation indexes were obtained, revealing the deformation mechanism of crushed rock mass. This result showed that the compression process of the crushed rock mass can be categorized into three stages: porosity compaction, crushing and filling, and stable compaction, and there is a good correspondence between the evolution of porosity and the relative crushing index. Under the same axial stress, the axial displacement and relative crushing index increase with an increasing gradation index, while the porosity and fractal dimension decrease. Under the same gradation index, the axial displacement, fractal dimension, and relative crushing index increase with increasing axial stress, whereas the porosity decreases. As stress increases, the mass of rock in the particle size range of 0–4 mm and 4–8 mm gradually increases, while the mass in the range of 16–20 mm gradually decreases. The increase in mass of the crushed rock in the particle size range of 0–4 mm is greater than that in the range of 4–8 mm. Under the same stress, the mass changes in the particle size ranges of 8–12 mm and 12–16 mm are smaller than those in other ranges. This study offers a theoretical foundation for managing overburden movement and ensuring the safe regulation of goaf.