Research On Directional Fracturing Mechanism Of Jet Perforating By Deep Hole Blasting In Hard Rock

With the increase in the depth and strength of coal mining,and the acceleration of the working face,the hard roof lag breaks,the ground pressure behavior is prominent,and the safety production of the mine is affected.Aiming at the problem of accurate orientation of the existing fracturing process,the technology of directional fracture and fracturing by deep hole charge blasting shaped perforation was proposed to achieve the goal of long-distance directional fracturing of hard rock deep hole,and the pressure relief effect of roof directional cut and stope was achieved.A series of studies have been carried out around the technology mechanism and technical practice of hard rock deep hole charge blasting shaped perforating technology,and the following research results have been achieved:(1)The impact failure characteristics of rock masses with cracks were analyzed through experiments,and the weakening effect of rock mass crack appearance and structure size on rock mass strength was obtained.The research conclusion is basically consistent with the influence law of static fracturing cracks in rock mass,but the free end under high strain rate loading shows obvious characteristics of reflective tensile failure.(2)The jet perforating by deep hole blasting in hard rock first manifests as highenergy convergence of explosives urges the high-speed impact of heavy metal particles to create cracks,and then the high-energy gas of composite explosives explodes growth cracks.The research shows that the thickness of the liner,the opening angle,and the explosive height of the charge have an important effect on the jet perforation and cracks.The axis of the liner is determined to be 20 mm,the opening angle is selected to be 60°,and the thickness of the liner is 1mm.The jet perforated directional penetration effect of the hole wall is the best.(3)The jet perforating by deep hole blasting in hard rock carried out on-site technical practice in the Yungang mine,the deep hole charge process flow of the shaped charge pipe is smooth,and the full length of the detonating cord is reliably detonated,the shaped charge perforating effect is good The crack density of the wall rock is small,and the opening size and extension length of the directional crack are large.The use of 1.5kg third-level explosives can achieve the 0.5m fracturing in hard rock.This paper has 76 figures,10 tables and 103 references.