Fractal Mechanical Characteristics of Irregular Top Coal Mass Fragmentation in Longwall Mining

In caving mining, irregular large top coal blocks formed due to overburden pressure and gravity often obstruct the drawing mouth, reducing efficiency, yet studies on their crush-ing characteristics remain limited. This study aims to investigate how fracture modes and geometry affect the fragmentation behavior of such coal blocks. Uniaxial compression tests were conducted on irregular top coal samples from a Gansu mine, with numerical simulations employed to analyze the influence of microscopic parameters. Results indi-cate that among four fracture modes, multi-peak and flat coal blocks exhibit better frag-mentation but higher crushing strength, while single-peak and blade-shaped blocks break unevenly with lower strength. Numerical simulations reveal that porosity affects both crushing strength and fracture direction concentration; elastic modulus influences break-ing time; bond stress impacts strength and breaking time; and loading rate alters crushing characteristics. The findings provide a basis for optimizing caving parameters and pre-venting blockages, contributing to improved mining efficiency.