Experimental Study on Key Parameters of Bidirectional Cumulative Tensile Blasting with Coal-Containing Composite Roof

Abstract

To improve the effectiveness of the directional-predetermined crack blasting in the weak and alternate composite roof, this paper took the coal-containing composite roof of the 12201 working face of Halagou Coal Mine as the engineering background, and based on the technical principles of roof cutting pressure releasing gob-side entry retaining, comprehensive used of theoretical analysis, field experiments and other means, carried out in-depth research on the shaped energy blasting method and parameter design of the coal-containing composite roof. The results show: Through theoretical analysis, in the process of shaped energy blasting, the air column in the hole can reduce the peak blast pressure, which can effectively prevent the weak surrounding rock in the hole from being damaged in the non-cumulative direction and enhance the pre-splitting effect. During detonation at the bottom, the instantaneous pressure in the blast hole is lower than that of detonation at the top, and the action time of blast pressure is longer than detonation at the top. When the buried depth of the explosive (near the blast hole) is less than the critical depth, a “V”-shaped blasting funnel will be formed after the rock blasting, and the critical depth is proportional to the charge. Through field tests on the charge quantity and the length of the sealing mud, when the blast hole depth is 6m, the charge parameters of “3+2+0+1” have a better effect of energy-concentrating blasting, and the crack rate reaches 87%. Besides, field tests have shown that when shaped energy blasting is carried out on soft and hard rock formations, the stemming separation in the shaped energy tube at the interlayer position can ensure the directional pre-cracking effect of hard rock, while effectively avoiding damage to the weak rock formation in the non-cumulative direction.