Study on parameters of blast hole spacing for gob side entry retaining by bidirectional shaped charge blasting

Abstract

In order to solve the problem of selecting reasonable blast hole spacing in gob-side entry retaining, based on the fracture forming mechanism of bi-directional shaped charge blasting, a mechanical model of combined hole shaped charge blasting is established, the influence parameters of shaped charge pipe are introduced, the rock crack propagation length after blasting is analyzed, and the calculation formula of blast hole spacing is deduced. Taking Qiuji Coal Mine as the engineering background, the reasonable blast hole spacing is calculated as 1.0 m. LS-DYNA software is used to simulate the crack propagation process of double hole shaped charge blasting with spacing of 0.8 m, 1.0 m and 1.2 m. The simulation results show that the peak stress of rock in the direction of shaped charge blasting is 2.6 times of that in the direction of non-shaped charge blasting at 0.2 m away from the center of the blast hole, and the crack in the direction of the connecting line of the blast hole is easier to expand; when the spacing of the blast holes is 1.0 m, the cracks between the two holes are completely connected and there is no vertical crack in the center of the connecting line of the blast holes. The field test in Qiuji Coal Mine shows that continuous cracks are formed in the holes after blasting with a spacing of 1.0 m, and the cracks between the holes are connected to form a cutting surface, which is consistent with the results of theoretical calculation and numerical simulation.

Keywords

• gob-side entry retaining
• bidirectional shaped charge blasting
• hole spacing
• crack propagation
• numerical simulation