Quantitative characterization of damage characteristics of coal using evaluation parameters considering the spatial structural characteristics of fractures

Stable underground tunnels and gas drainage boreholes are important guarantees for safe and efficient coal mining. The stability of these structures is closely related to the mechanical properties of coal and rock damage. Accurate quantification of coal and rock damage factors is a prerequisite for objective evaluation of damage mechanics. In order to study the relationship between coal and rock damage factors and fracture structure parameters in coal, the "CT scanning + Avizo image processing" method was used to reconstruct the three-dimensional spatial morphology of fractures in coal samples from the Yuwu Mine in Shanxi Province, China. The construction of a parameter system for evaluating the spatial structure of fractures represents the three-dimensional composition of fractures. Combined with uniaxial compression tests, a mathematical model for coal damage factors based on fracture spatial structure parameters was established, and the influence of fracture parameters on the mechanical properties of coal damage was discussed. The results show that fractal dimension, spatial attitude factor, and discreteness can respectively characterize the complexity of fracture morphology, the impact of fracture spatial angles on compressive strength, and the spatial discreteness of fractures; coal damage factors are positively correlated with porosity and spatial attitude factors, and negatively correlated with fracture fractal dimension and fracture discreteness. The mathematical model of coal rock damage factors established in this study has a correlation with experimental test values that is 0.3174 higher than that of traditional damage factor models, which can more objectively characterize the mechanical damage characteristics of coal rock. In summary, this study provides an efficient and accurate method for the quantitative characterization of coal body damage factors considering the characteristics of fracture space structure.