Mechanism of floor rockburst and blasting parameter optimisation for high-stress roadway subjected to severe dynamic loads

For mining in the north-west of China, coalburst frequently occurs when subjecting to horizontal tectonic stress and strong dynamic loading. Experiment, theoretical analysis, numerical simulation and engineering test were performed to investigate the large-area rock burst floor failure in 208 working face. Based on the elasticity theory and the catastrophe theory, the influence mechanism of high stress and dynamic loading was analyzed, and the principle of coalburst mitigation by blasting was studied. The deformation, displacement and surface acceleration of the surrounding rock of roadways caused by dynamic loading with and without floor blasting were analyzed. The horizontal stress should be taken into account to avoid exacerbating the damage to the tunnel or the coalburst due to asymmetric damage. The influence of blasting hole angle, charge density and uncoupling coefficient on the pressure relief effect of floor blasting were simulated and analyzed. The results show that the high horizontal stresses tend to exacerbate the asymmetric damage after floor blasting, inducing coalburst. The hole angle determination is the premise of the design of the floor blasting parameters, and its adaption to the natural fracture or bedding plane of the rock mass should be considered to improve the blasting pressure relief effect. The optimal interval of the uncoupling coefficient is 1.46, beyond which the damage zone and crack extension length are significantly larger than the other. The charge density is positively correlated with the damage zone of rock mass, crack propagation length and surrounding rock stress, but the strengthening increase is not obvious under the larger charge density. The floor deformation was reduced by 22% to 61% after floor blasting optimisation parameters. During field implementation, no microseismic events with energy more than 1×10⁵ J were observed and the proportion of tremors in floor reduced significantly. The results can be used as a reference for the design of floor blasting parameters for high-stress roadways subjected to severe dynamic loading.