Coal damage and failure from shaped charge blasting with an empty hole under high ground stress

The effectiveness and safety of blasting operations used to increase gas permeability in the coal seam are compromised by the high crustal stress in deep coal mining. In order to increase the effectiveness of blasting cracking and reflection enhancement of coal seams, the crack propagation law and damage characteristics of high ground stress coal bodies under the action of shaped charge blasting coupled with empty holes are studied through the method of theoretical analysis combined with blasting simulation tests. The results demonstrate that shaped charge blasting can generate a directional cutting impact on coal via shaped charge jets, improve the efficiency of explosive energy utilization, and focus energy in a particular direction. The free surface impact from the void amplifies damage and promotes crack propagation in the coal body over a distance. In the blasting simulation experiment, elevated ground stress results in the re-compaction of the ruptured fissure, especially when the coal body undergoes significant crushing from standard blasting methods. Shaped charge blasting with vacant holes yields an average damage value that is 1.26 times and 2.1 times larger than that of conventional blasting, as determined by damage assessments by resistivity and ultrasonic wave velocity measurements. The results of this study have significant social consequences for safeguarding mining production safety. Theoretical and experimental principles are established to enhance the permeability of coal seams subjected to elevated ground stress, augment blasting efficiency, and optimize blasthole use.