Characteristics of fractal evolution of sectional fractures in tectonic coal assemblages with different loads based on CT scans

To study the fractal structure of planar cracks in tectonic coal composites during the damage process under load, uniaxial loading tests were conducted on the specimens of structural coal composites as the research objects. The fractal characteristics of the surface fracture propagation of the loaded structural coal composite specimens were quantitatively characterized by using CT scanning equipment and Avizo image analysis software. The results shown that the transverse fractal dimension, the longitudinal fractal dimension and the fracture pixel ratio increased linearly with the increase of load. The changes in fractal dimensions and fracture pixel ratio were mainly concentrated in structural coal. The longitudinal cleavage dimension and pixel ratio shown an upward-downward-upward trend with the variation of the load. Under the action of continuous loading, the cleavage structure of the structural coal pores was destroyed first. When the stress at the tip of the crack was greater than that at the interface, the penetration effect of the crack could propagate. Meanwhile, the increase in stress led to the generation of interfacial additional stress at the lower interface, and the cleavage developed downward, resulting in the overall fracture of the specimen. The above research results could provide theoretical support for the prevention and treatment of coal and gas hernias.