Mechanical properties and failure behaviors of the coal-rock combination with blasting-induced cracks: A numerical study

: With coal extraction advancing into deeper levels, coal bursts induced by sudden energy release from thick-hard roof present severe safety and economic challenges. To deeply reveal the mitigation mechanism of roof deep-hole blasting for coal bursts, an innovative hybrid LS-DYNA/PFC modelling framework was developed to quantitatively investigate the governing role of blasting-induced cracks on the mechanical and failure behaviors of coal-rock combinations under mining stress. The dynamic blasting simulations in LS-DYNA program first characterized the detonation pressure attenuation and blasting cracks characteristics. Subsequently, the dynamic blasting and static loading for the coal-rock combinations were simulated successively in the PFC program. Results demonstrate blasting cracks in the roof rock fundamentally degrade coal-rock combinations, resulting in significant reductions in peak strength (by 21.3-43.7%) and elastic modulus (by 7.1-13.7%), alongside drastic decreases in maximum strain (by 13.0-21.4%) and the impact energy index (by 22.5-81.3%). The systematic weakening of load-bearing capacity, energy storage efficiency, and dynamic failure propensity confirms roof blasting as an effective strata-control strategy for coal burst mitigation. Compared with the coal-dominated instability failure of intact coal-rock combination, the blasting-fractured samples exhibited an approximately "triangular" fracture surface where secondary fractures nucleated at stress-concentrated blasting crack tips in roof rock, then propagated toward coal interfaces along the direction of the blasting cracks. Furthermore, blasting cracks reshape the energy "storage-release" path of the coal-rock system. By reducing the total amount of releasable strain energy (by 28.5 - 60.6%) and transforming the concentrated release mode into a progressive and multi-stage dissipation mode, the impact intensity of samples was significantly alleviated. Moreover, the parameters of blasting cracks (distribution length and density) and proximity to coal critically influence these effects. These findings establish a quantitative, mechanistic basis for optimizing roof blasting parameters to prevent coal bursts.