Application Of Directional Fracture Controlled Blasting Technology In Roadway Excavation Of Zhongtai Mining Industry

Rock directional fracture controlled blasting is a new technology based on traditional bare face blasting technology,of which slit pack blasting is widely used in coal mines for its ease of construction,economy and safety.This paper proposes a directional fracture controlled blasting solution for hard rock roadways in the Hebi mining area,based on a rock tunneling project,to reduce over-and under-excavation and improve the utilisation rate of the roadway holes,while also effectively reducing the number of secondary cracks on the rock around the holes and improving the stability of the surrounding rock.In this paper,based on existing research,research on directional fracture controlled blasting technology is carried out.Through a combination of theoretical analysis,similar model tests,numerical simulations and field test applications,the research method is used to reveal the mechanism of directional fracture controlled blasting and to obtain the optimum blasting parameters for slit pack blasting,and the research results are applied to coal mine roadway forming:(1)Based on the elasticity theory,fracture mechanics seam formation theory,Griffith brittle damage theory and the composite "air wedge effect" damage theory on the directional fracture seam formation mechanism,the seam package explosion stress field mechanical analysis,the stress in the plastic zone stress field in the non-shear direction is less than the stress in the direction of the seam.The controlled blasting process of directional fracture of the slit package can be broadly divided into three stages,namely the initial shock wave formation stage from the detonation of the explosive to the slit tube,the initial directional fracture formation stage and the fracture development stage.(2)The analysis was carried out using LS-DYNA/ANSYS 14.0 software with blasting method and slit width as independent variables and blasting effect as dependent variable.The results showed that slit pack blasting was able to reduce the number of random cracks in the vicinity of the gunhole wall and form directional initial cracks along the direction of the slit.At a slit width of 6 mm,the slit tube provides both the crosssectional area and the strength of the gas jet;it also ensures that the gas forms an aggregate effect within the slit tube and delivers energy to the tip of the jet.(3)The average damage variable of slit pack blasting on cement mortar specimens was 76% of that of normal pack blasting.In slit pack blasting,when the proportional distance position was certain,both the slit direction and the vertical slit direction showed that the average damage variable of the first row reached a great value,and the average damage variable gradually decreased with the increase of the depth of the shell hole.When the gun hole spacing was 16 cm,the slit pack blast profile was smooth and the degree of directional crack expansion was good.(4)Field trials have shown that: slit pack blasting effectively improves the flatness of the excavated section of the roadway,increases the half-hole rate,with a maximum of92%,and smooths the outline of the roadway after blasting;the average linear overexcavation decreases by 59% to 0.169 m compared to normal pack blasting;increases the spacing between the perimeter eye shell holes,saves explosives,and reduces the amount of explosives per cubic metre by 20%,with more significant economic and safety benefits.The effect of directional fracture is more obvious.51 figures,25tables,and 106 references.