Study on the coupling mechanism of shaped blasting and empty hole to crack coal body

Abstract

In this study, the mechanism of cracking under the coupling effect between the use of shaped blasting and deployment of empty holes was explored through theoretical analyses, numerical simulations, and experiments to determine the effects of empty holes on the traveling characteristics of blast-induced stress waves, the propagation patterns of detonation cracks, and the evolution characteristics of blast-induced damage. The results indicated that shaped blasting concentrated energy in a fixed direction to enhance the efficiency of explosive energy use, and the resultant shaped jet created a directional, cut-like crack in the coal layer of specimens. The additional free face provided by empty holes increased the tensile stress, the level of damage in areas located far away from the blast hole, and the propagation capacity of the crack. The levels of specimen damage in shaped blasting that were determined using the resistivity and ultrasonic wave velocity were 1.2 and 1.7 times higher, respectively than those in ordinary blasting. The tensile strain at the empty holes was 2.73 times higher and the static loading phase was 0.9 μs longer in shaped blasting than in blasting sites without empty holes. The coupling effect between shaped blasting and empty holes substantially improved the effectiveness of the blasting operation in creating directional cracks. This study provides a theoretical and experimental basis for directional blasting techniques; reveals an effective approach that enhances the efficiency of blasting, improves the effectiveness of blast holes, and limits blasting disturbance; and offers socially valuable insights into safe and efficient production practices.