Fracture and porosity evolution of coal under uniaxial compression: An in-situ X-ray tomography study

Abstract

To investigate the meso-structure evolution and fracture mechanism of coal under uniaxial compression, an X-ray three-dimensional scanning microscopy in-situ loading test bench was used to conduct a uniaxial compression test of coal. CT data were obtained under different strain conditions and combined using 3D visualization software. According to the surface porosity under different axial forces shows stages in the Z axis, the 3D reconstruction of coal was divided into three regions to compare its structural evolution law. The results show that the uniaxial compression of coal presents staged fractures, and the distribution characteristics of fractures and pores are closely related to internal stress propagation. With the axial force loading, the internal fractures continued to expand, accompanied by the generation of micro-fractures. The development degree of penetrating fracture and lateral strain in region 1 were always higher than in region 2 and region 3, which is more obvious after the scan D; During the whole process of uniaxial compression, the three regions interacted with each other, and the energy transferred between regions has a “hysteresis”. The failure response of region 1 to axial force was earlier than that in region 2, and region 2 was earlier than region 3. However, the fracture evolution behavior of the same region, the three regions showed consistency; After scan D, the meso-structure changes of region 1 were more significant than the other two regions; The coal was locally deformed and destroyed under the action of axial force, resulting in isolated pores and micro-fractures. The spatial distribution of pores and fractures, the existence of micro-fractures and the interaction among different regions aggravated the uneven distribution of axial force in coal, which has a great influence on the fracture process of coal, so that the failure of coal present stages.