Abstract:
The roof pressure relief of strong impact working face is an important prerequisite for the safe mining of deep coal mines. The blasting pressure relief technology has an important influence on the overburden rock migration and energy release. In this paper, a new method of pressure relief named double cut-one blasting is proposed. The static loading control test of post-explosion rock mass is carried out by using prefabricated rock samples. The energy dissipation characteristics of prefabricated rock samples are analyzed by using pressure-displacement curve. The strain evolution process is recorded by digital image correlation method (DIC) strain field, so as to analyze the deformation and failure characteristics of prefabricated rock samples. Combined with acoustic emission monitoring data, the dynamic damage evolution characteristics of crack initiation, development, expansion and penetration in rock mass are analyzed. The specific conclusions are as follows: compared with complete rock samples, peak pressure of two cut-one blasting rock samples is reduced by 68.19%, and the ability to absorb the external load to do work (energy) is reduced by 81.89%; energy release band can not only effectively reduce peak pressure, but also dissipate more energy in post-peak step-like downward trend. The two cut-one blasting changed the crack initiation and propagation mode of rock samples in control group, which is generated from upper-lower ends of crack and extended to the middle, transformed into the end of explosive crack and extended to upper-lower sides. The failure of rock specimen is the comprehensive effect of cutting, hole and explosion crack. The energy release zone formed by the three plays a guiding role in generation and penetration of cracks, and plays a leading role in the process of energy dissipation. The energy is consumed by internal deformation adjustment, finally the “X-type” fracture surface is formed. The ringing count and energy curves of two cut-one blasting rock samples show the characteristics of multi-stage stepped rise before the peak. Among them, the peak value of ringing count increases by 27.66%, while peak value of energy decreases by 53.43%. The ringing count and energy prove that two cut-one blasting energy release band can gradually transition from a few large energy events to multiple small energy events. The three-dimensional positioning of the acoustic emission signal of the double cut-one blasting rock sample is concentrated in 40 - 60 mm energy release band in the middle, indicating that the drilling and explosion fissures cause the stress concentration phenomenon in the rock sample earlier and form a concentrated source of damage. The energy-relieving buffering effect of the double cut-one blasting energy release band is fully verified by static loading test, which is of great significance for the pressure-relieving and anti-scour engineering of the strong impact working face in deep coal mines.