ABSTRACT To address the limited fracturing range produced by liquid‐nitrogen freezing and the insufficient permeability enhancement achieved by blasting in low‐permeability soft coal seams, this study proposes a coupled liquid‐nitrogen freezing and blast‐induced permeability enhancement method. Uniaxial compression and Brazilian splitting tests were performed on coal samples with varying water contents and freezing durations to quantify the mechanical modifications induced by freezing. These parameters were incorporated into a Riedel–Hiermaier–Thoma (RHT) constitutive model to simulate dynamic damage evolution and fracture propagation during blasting. The results show that compressive strength and elastic modulus increase initially and then decline with either prolonged freezing or increasing water content. The most favorable mechanical state occurred at 12% water content and 60 min of freezing, where compressive strength and elastic modulus increased by 109.8% and 143.8%, respectively, whereas tensile strength decreased by 55.8% relative to unfrozen dry coal. This combined strengthening–weakening effect reshapes the coal's load‐bearing structure and promotes tensile‐dominated failure. Blasting simulations further reveal that, for dry coal, both the proportion of fissure zone volume in total damage and crack length first increase and then decline with freezing duration, reaching their maxima at 60 min, where they rise by 9.9% and 245.0%, respectively, compared with unfrozen coal. For samples with different water contents frozen for 60 min, both parameters display the same trend and peak at 12% water content, with fissure zone volume proportion and crack length increasing by 7.7% and 50.0%, respectively, relative to dry coal.
Liang et al. (Mon,) studied this question.