Abstract
In order to explore the reasonable spacing of charge holes in empty-hole directional blasting, based on the action mechanism of empty-hole directional blasting, the influence of charge hole spacing on crack propagation is studied, the calculation formula of charge hole spacing is deduced, and the blasting excavation process in Shijiazhuang South Ring Expressway Tunnel is simulated by finite element software. The results show that by setting empty holes on both sides of the charge holes in the peripheral blasting, the guiding cracks can be formed in the connecting direction between the empty hole and the charge hole, the propagation of cracks in other directions can be suppressed, and the spacing of charge holes can be enlarged. Reasonable charge hole spacing is very important to realize the effect of empty-hole directional blasting; the spacing is small, the rock will be overbroken, and the utilization ratio of explosives is reduced; large spacing, the guiding effect of empty holes is weak, and the effective directional cracks cannot be formed. The spacing between charge holes is closely related to the mechanical properties of rock, detonation parameters of explosive, and aperture of the charge hole and empty hole. According to the simulation results of crack propagation in different spacing, the blasting performance is the best when the charge hole spacing is 800–1000 mm, which is completely consistent with the theoretical calculation result of charge hole spacing 948 mm.
Highlights
Ordinary peripheral blasting can form cracks between the blastholes, but a large number of random cracks will be generated in other directions around the holes, leading to the decrease of the stability and integrity of surrounding rock [1]
According to the theory of elastic mechanics, Liu et al [7] studied the mechanism of the empty hole effect in cut blasting and concluded that the effect of stress concentration will be produced by the empty hole
The effect of the empty hole in directional blasting is theoretically analyzed, and the influence of charge hole spacing on blasting crack propagation behavior is studied; the charge hole spacing is calculated by theoretical analysis and numerical simulation, and it can be concluded that
Summary
Ordinary peripheral blasting can form cracks between the blastholes, but a large number of random cracks will be generated in other directions around the holes, leading to the decrease of the stability and integrity of surrounding rock [1]. As for the research of the empty hole in blasting engineering, Mohanty [4, 5] proposed and verified by experiments that the radial controlled cracks can be produced by setting the empty hole on both sides of the charge hole, and the directional blasting effect equivalent to that of notched blasting is obtained. Li et al [8] deduced the formula concerning on the empty hole effect under blasting stress by using elastic mechanics theory and improved and verified the calculation model of the empty hole effect. Based on the action mechanism of empty-hole directional blasting, the theoretical analysis and numerical simulation method are adopted, the influence of the spacing between the charge holes is analyzed, the calculated formula of the charge hole spacing is proposed, and the reasonable charge hole spacing of the blasting excavation of the Shijiazhuang South Ring Expressway was obtained
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