Empty-hole effect on fracture propagation under blasting load

In this study, we present a simple and effective method to improve the fragmentation efficiency of rock-like materials. An empty hole is arranged reasonably beside the charge hole in the specimen. Through the effect of empty hole, the explosion load produces stress concentration on the line between the charge hole and the empty hole, so as to achieve the effect of directional cracking. In this paper, the influence of the crack direction and the distance between the charging hole and the empty hole on the crack growth is analyzed through experiment and numerical simulation, and the strain around the empty hole is measured under different charging hole layout, and the explosion effect is compared. The results show that when the empty hole is located at fracture zone, the empty hole is able to control the direction of crack growth effectively. It plays a crucial role in directional fracture, and the strain is the maximum in this situation. When the empty hole is located at crush zone and elastic zone, it was ineffective in directional fracture, because of the stress field surrounding the empty hole and the pressure field formed by detonation gas at crack tip fail to reach the requirement of the crack growth. By analyzing the air pressure measurement during blasting, it can be concluded that the optimum distance of the empty hole is 60 mm, achieving the dramatic effect of air pressure fluctuation. In application of coal mine roof weaken in Huaibei Mining Group, the empty holes play an important role in advanced pre-splitting blasting.