Study on damage characteristics and fracture mechanisms of coal under high stress environment during blasting

When using blast fracturing technology to enhance the permeability of deep coal seams, high in-situ stress makes it difficult for cracks to propagate between blast holes, posing a significant challenge for gas management in deep mines. This study combines theoretical analysis and numerical simulations to investigate the crack propagation behaviour and coalescence mechanisms of coal under various in-situ stress conditions. A theoretical model is first developed for single hole blasting to analyse the static stress distribution around the blast hole and the dynamic stress changes under blast loading. The influence of tangential static stress on crack propagation and coalescence is further investigated for simultaneous double hole initiation. The calibration of parameters in the Riedel-Hiermaier-Thoma (RHT) model for coal is performed using empirical formulas and dynamic mechanical tests, with numerical model validation conducted against fracture size distributions obtained from laboratory tests. Finally, the crack propagation and coalescence induced by single blasting and double hole blasting under varying in-situ stress conditions are simulated. The numerical results show that in-situ stress significantly suppresses both the length and number of blast-induced cracks, reducing the fractal dimension of coal damage. For double hole blasting, an angle of less than 30° between the blast hole connection line and the major principal stress direction facilitates the formation of inter-hole crack coalescence zones between the holes. Based on theoretical analysis and numerical results, it is suggested that aligning blast holes along the principal stress direction enhances permeability improvement in coal seams under high in-situ stress conditions. This study not only provides new insights into the mechanisms of crack propagation in coal blasting but also offers guidance for optimizing coal seam permeability enhancement under high in-situ stress conditions.