Relief Mechanism of Segmented Hole Reaming and Stress Distribution Characteristics of Drilling Holes in Deep Coal Mine

Abstract

As the mining depth increases, in underground tunnels, caverns or pillar goaf, a rock burst is one of the important accidents that threaten mine safety. Drilling pressure relief becomes one of the main means of preventing rock bursts, which affect the mechanical properties and stability of the coal and rock in underground excavations. However, the surrounding rock of the roadway or the coal body is usually broken, and the pressure relief of the large-diameter borehole will affect its support. A segmented hole-reaming technology is proposed and applied in a coal mine in China. A pressure-relief mechanic model of segmented hole reaming was built. The coal sample had an elastic modulus of 0.35 GPa, the UCS and UTS were 17.4 MPa and 1.41 MPa, the Poisson ratio was 0.27, the cohesive force was 2.81 MPa, and the friction was 23.7°. The pressure relief range of the boreholes with different diameters, horizontal in situ stress coefficients, cohesive forces, and friction angles were analyzed. When the drill hole was increased from 120 mm to 200 mm, the pressure relief range was increased by 57.1%. The stress distribution of the staged reaming and pressure-relief drilling was also obtained. In the vertical direction, the vertical stress of the borehole first decreased and then was restored to the original rock stress area, and in the horizontal direction, it first increased and then was restored to the original rock stress area. A CMS1-6200 segmented drilling rig was used to construct the pressure relief hole. The weight of the drilled pulverized coal was monitored at different depths. The results showed that the amount of pulverized coal in all of the drilled holes was less than 3 kg/m, indicating that the effect of reducing the pressure relief is obvious. The study is of great significance to research the pressure relief range, mechanical characteristics and stress distribution of segmented hole reaming; it also provides insight into the rock burst prevention and the design of drilling in the mine site.