Microscopic fracture evolution and propagation mechanism of coal with high coal burst liability

The key to preventing and controlling rockbursts is to clarify the microscopic fracture evolution law and expansion mechanism of coal with high coal burst liability. Meanwhile, there is a black box problem in the process of internal crack propagation in coal under external loads, making it difficult to directly observe the coal's internal crack network. Consequently, the in -situ loading scanning comprehensive analysis system is employed in this study to conduct experimental investigations on the fracture evolution of coal under uniaxial compression. Additionally, the internal crack network of coal under varying stress states is quantitatively analyzed. This research also uncovers the crack propagation mechanism in coal prone to high coal burst liability. The results show that the precursor point for rapid crack propagation under uniaxial compression load occurs at approximately 80 % of peak stress, signifying that the failure of this coal type is abrupt. The proportion of crack image area and the volume, surface area, and fractal dimension of the cracks exhibit a trend of initial decrease, stabilization, slow increase, and then a rapid surge. The changing trends of these indicators can quantitatively reflect the expansion and evolution characteristics of internal cracks in coal bodies. In addition, when encountering gangue, two phenomena are observed during crack propagation: penetration through the gangue and diversion around it. This shows that gangue significantly impacts the propagation mode of internal cracks, elucidating the evolution mechanism of crack propagation in coal with high susceptibility to coal bursts from a microscopic viewpoint.