Three-dimensional visualization and quantitative characterization of coal fracture dynamic evolution under uniaxial and triaxial compression based on μCT scanning

The characteristics of pore-fracture networks in coal seams and their evolution under compression are important for exploration and development of coalbed methane (CBM) and for the forecasting of coal dynamic disasters. Significant process has been made in fracture characteristics of rocks, however, the visualization and detailed quantitative characterization of real-time dynamic evolution of micro fractures in coal under triaxial compression are poorly understood. In this study, uniaxial and triaxial compressive tests and real-time CT scanning tests on anthracite were carried out using X-ray micro-Computed Tomography (X-ray μCT) equipped with the triaxial compression facility. The image processing technique, three-dimensional reconstruction and statistical principles were employed to extract geometric morphology, fracture growth and evolution. The results showed that confining pressure had certain inhibitory effect on the development of fractures in coal and also had effect on the forms and spatial distribution features of failure fractures in coal. The gray value, the fracture volume and also CT porosity could be the quantitative damage variable to evaluate the damage evolution of coal. The qualitative and quantitative analysis of fractures in anthracites indicated that their damage evolution process could be divided into three phases under uniaxial test and four phases under triaxial test, the precise degree of each phase was also given. The image and stereology analysis results reflected the microscopic fracture evolution process of anthracites under compression test agree well with the experimental results. The work of the paper is of great academic and realistic significance for further studies of coal structure and their dynamic evolutionary mechanism under loading using X-ray μCT.