Research Anti-Impact Mechanism of Roof Presplitting Blasting in Deep Composite Thick and Hard Key Strata

As an important means to control the hard roof, presplitting blasting is the main measure for controlling rock burst disaster in the key strata of the deep mine in the west. Taking the typical thick and hard key layer, Menkeqing Coal Mine as the analysis object, the mechanical and FLAC3D numerical models of roof presplitting blasting energy release are established. The structural characteristics and evolution laws of key layers during mining operations are analyzed, and the mechanism of rock burst behavior in thick and hard key layers is revealed. The influence of combined blasting scheme on the evolution law of roof stress field and energy field was studied. The engineering practice and the control effect of presplitting blasting on roof were carried out and evaluated. The results show that (1) in view of the characteristics of "difficult to collapse and strong energy storage" of composite thick and hard key strata in a deep stope, the targeted low-high combined blasting measures can realize the transformation of overburden structure from "F" type to "Gamma" type, effectively shorten the exposed length of key strata, reduce the in-plane static load stress, weaken the dynamic load strength, and reduce the impact risk. (2) After adopting the low-high combined blasting measures, the maximum vertical stress reduction on both sides and above the goaf is 70% and 90%, respectively, and the energy release is up to 106 J, which greatly reduced the stress concentration inside the coal body and weakened the energy intensity when the overlying strata structure in the goaf was broken. (3) The total energy and frequency of microseismic events during the mining period, as well as the pressure strength and pressure step of the support, were significantly reduced. The effectiveness of the combined roof presplitting blasting technology in preventing and controlling rock burst was verified by FLAC3D numerical simulation and field monitoring. The research results have been successfully applied to the Menkeqing Coal Mine.