Propagation behavior of coal crack induced by liquid CO2 phase change blasting considering blasting pressure effects

To investigate the crack propagation mechanisms in low-permeability coal seams induced by liquid CO2 phase change blasting under different blasting pressures, this research presents an experimental study conducted on a small liquid CO2 phase change blasting test system. The failure mode, crack morphology, and distribution characteristics of the coal rock model specimens under different liquid CO2 phase change blasting pressure were revealed, analyzing the crack shapes and expansion process. The results show that with increasing blasting pressure, both the number and complexity of cracks significantly increase under liquid CO2 phase change blasting, evolving from simple linear cracks to more complex multi-directional networks. Furthermore, the process of crack generation and expansion during liquid CO2 phase change blasting in coal and rock is controlled by the interaction of shock waves and quasi-static stress resulting from high-pressure CO2 phase transition in the borehole. Cracks form in distinct zones: the broken zone, where shock waves cause severe crushing near the borehole; the crack zone, where quasi-static tensile stress drives crack propagation. Higher confining and CO2 blasting pressures increase crack propagation. The research results offer valuable insights for optimizing blasting design in liquid CO2 phase change fracturing.