Control Effect Of Mechanical Properties On Borehole Pressure Relief In Coal Seam

At present, large diameter borehole distressing is an important relief measure for the prevention and control of rockburst. By means of theoretical analysis, numerical simulation and industrial test methods, the paper analyzed pressure relief mechanism of the large diameter borehole, studied the pressure relief rules of drilling parameters, studied the control effect of geological occurrence conditions on borehole pressure relief in coal seam. The research conclusions were applied to the field practice to analyse the actual effect of anti impact and pressure relief, provide the theoretical basis and reference for large diameter borehole pressure relief.Through theoretical analysis of the deformation and failure mechanism of surrounding rock, the calculation formula of the coefficient of drilling hole is obtained. The surrounding area of drilling hole is divided into the residual strength zone, plastic zone and elastic deformation zone from the near to the distant, and the calculating formulas of the range of three strength zones are given. The basis for determining borehole pressure relief parameters is established, the influence range of borehole pressure relief is analyzed, and the pressure relief ring is determined. The pressure relief range decreases with the increase of the elastic modulus of the coal seam, and increases with the increase of the Poisson’s ratio of the coal seam.By means of the numerical simulation software, the spacing and the aperture of borehole is approximately linear relationship, with the increase of the borehole diameter, the spacing also increases accordingly. The relationship between the ratio of spacing and diameter and the diameter of the borehole is multiple function:7 4 3N3.95792 10 D0.00026455D-= ′-2+0.0651145D-6.9775 D +283.05754. With the increase of borehole depth, the stress concentration is transferred to the end of the drill hole. In the same pressure relief conditions, the effect of pressure relief in soft coal seam is better than hard coal seam, the pressure relief effect in deep coal seam is better than shallow coal seam. Besides, By means of the numerical simulation software, the relationships between reasonable spacing of borehole and the mechanical parameters of coal seam is established, in the premise of ensuring the pressure relief effect to improve the efficiency of the drilling relief, the relationship between the spacing of borehole and the elastic modulus of coal seam is negative exponential function, the relationship between the spacing of borehole and Poisson’s ratio of coal seam is logarithmic function. When the borehole aperture is 200 mm, the fitting formula of maximum borehole spacing in the specific coal seam parameters is obtained:-0.3861.411 0.418 ln 1.3964EmaxD =e +n +. The borehole depth should be achieved the original stress peak position when implementing destressing boreholes in the coal seam, at this point, part of high force at the original peak position releases to the drilling hole, the other part is transferred to the end of borehole in the deeper surrounding rock.The research conclusions were applied to the-1000 Xiyi mining area in Zhangshuanglou Coal Mine, to test the effect of pressure relief. The coal dusts’ quantity and CT inversion results after pressure relief showed that stress was at a lower level in relief area, no impact appeared. The taken destressing measure of large diameter borehole achieved good effect of pressure relief, played a discharge pressure relief role, achieved the purpose of preventing rockburst in coal mine, and proved that the drilling parameters of borehole are reasonable and scientific.