| Coal and gas outburst occurs at a higher probability when uncovering coal in cross-cut, and the large number of coal and gas that comes along with it makes a serious damage, which seriously affect the normal production of coal mine. Shunfa mine of Henan Hongfu coal Co., Ltd is going to uncover Ⅱ1 coal seam during the period of its hoisting system upgrading. Mylonitic coal, whose intensity is very low, is widely developed in that area. Gas content of the coal seam is extremely big, which resulted to great danger of outburst. On the history of Shunfa coal mine, coal and gas outburst occurs when uncovering coal in the air shaft and auxiliary shaft, after taking measures of intensive emissions drilling. And because of this, it is necessary to study integrated outburst eliminating techniques that apply to uncovering mylonitic coal in crosscut.According to the combined effects hypothesis of coal and gas outburst, this paper established a numerical model, which has same conditions of in-situ stress and gas and different coal structures. Then the paper studies the features of stress distribution and displacement of top coal when uncovering coal in crosscut under the original conditions. The results show that mylonitic coal has a lager range of outburst and a bigger top coal displacement. Before the uncovering, stress of primary structure coal drops uniformly. But on the contrary, the stress value of mylonitic coal is more dispersed, part of which appears stress concentration. This means that pressure relief unevenly. With the outburst proceeds, peak stress transfers to the deep area of coal. And the peak stress of mylonitic coal is larger than that of primary coal. Thus, obtain a targeted outburst eliminating measure that is suitable for t mylonitic coal, which is the integrated use of hydraulic punching, pre-extraction of coal seam gas and coal solidification measures. The regional outburst prevention measures’ control area of mylonitic coal must be lager than that of primary coal. And it is more important to remove the in-situ stress effectively than to release gas in coal.A numerical model was established to simulate the hydraulic punching. Compared the change of acoustic emission and stress value of coal, then determined the reasonable pressure for punching. The results showed that it is able to reach the purpose of stress relief when the pressure is 4MPa. With the hole arranging spacing reducing and pore diameter increasing, the situation of stress concentration in the coal decreases. And it can effectively avoid stress concentration when the hole spacing is 4m and pore size reaches 1m. The suitable hydraulic punching measure for mylonitic coal should be small punching pressure and small hole arranging spacing. On the basis of this, we designed 165 drilling holes to extract gas from coal seam, 48 hydraulic punching holes included.Then we investigated the effect of hydraulic punching. The total amount of coal that rushed out of the hydraulic hole is 571.7tons. And the maximum amount of a single hole reached 29.1 tons. After punching, pore diameter became 7.15 to 20.40 times than before. Gas drainage density and gas drainage volume increased significantly. Accumulated volume of gas extraction is 65631.2m3. The rate of pre-pumping reaches 70.5%. Measured residual gas content were less than 6.5 cubic meters per ton, which means the regional measures is effective to eliminate the outburst danger of coal seam.A numerical model which simulates crosscut coal uncovering after taken regional measures was established to study the outburst danger. Results showed that a large range of rupture occurred on both sides of the roadway. And the displacement of top coal is one nineteenth of before. To optimize the design of numerical model, we reinforce the roadway on both sides of the coal. And results showed that it reaches a better effect when the thickness of punching zone is 10 m and solidification zone 2m. |
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