Fracture evolution of coal under uniaxial compression based on X-ray microscopic imaging

In order to study the evolution of the microstructure characteristics of coal with increasing axial stress, this paper used NanoVoxel-3502E X-ray three-dimensional microscope and Deben in-situ loading test rig to carry out uniaxial compression tests of coal to obtain CT data under different strain conditions, Combined with the three-dimensional visualization software AVIZO, extracted the pores and fractures of the coal sample, studyed the pore and fracture distribution characteristics of the coal sample, and statistically analyzed the microscopic parameters of the number of pores, sphericity, and coordination number, curvature, thickness and other meso-structure parameters. It revealed the spatial distribution characteristics of the mesostructure of the coal sample under uniaxial compression and its distribution law over time, and the evolution law of the mesostructure with the axial stress. Studies have shown that small fractures appear in large numbers from 20 N to 732 N, and the number of pores increases. During the process from 431 N to 732 N, the concentrated distribution range of pore sphericity became narrower. Some pores and fractures gradually merged into the fracture network, and some pores and fractures were compressed. Part of the pores were compacted at 732 N, resulted in a reduction of 90,000 pores. The curvature of the fractures gradually increased, the fractures gradually became thicker, and the coordination number concentration ratio was higher. It also showed that the coal sample was internally connected. 732 N was the pinnacle of fracture network development. When the axial force reached 1100 N (peak), a complex fracture network was formed. With the advancement of the uniaxial compression process, although some pores and fractures were compacted at 732 N, due to the increase in axial force and residual load, the increase of pores and fractures was an inevitable trend, and there were still small pores and fractures after the peak, but the post-peak fractures were thinner, and the sphericity was more concentrated in 1.5-2.0. The curvature of the interconnected fractures was generally higher at the edges of the fracture network, the edges of the fracture network were fracture development zones. This paper provided a feasible technical means for studying the temporal and spatial evolution of coal samples, and has practical significance for interpreting the temporal and spatial evolution of the meso-structure of coal.