| The occurrence of coal and gas outburst accidents is often be seen in the process of excavating in coal roadway. For a low permeability single coal seam prone to gas outbursts, pre-drainage of gas is difficult and inefficient during the coal roadway driving. Mine pressure researches showed that that there was a stress relaxation zone beside goafs. In the pressure relaxation zone, the balance of in-situ stress and gas pressure are destroyed, original fractures opened or expanded. As a result, the danger of coal and gas outburst is gone. So that in this zone coal roadway can be driven fast. In order to accurately determine the pressure relaxation zone and tunnel fast within it, this paper used many methods to determine the pressure relaxation zone. Finally, the paper synthesized all the results to determine the width of the pressure relaxation zone.There are many ways to determine the width of the depressurization zone now. But results which were determined by the former ways had a big difference with the actual results because of the complicated and variable affecting factors which had a influence on the width of the pressure relaxation zone. This article was based on a theoretical analysis of the feasibility of such a method preventing outburst by tunneling in the pressure relaxation zone. Then combining with the field trial data such as gas content, gas pressure, initial speed of gas emission from borehole, value of drilling cuttings weight, desorption index for drilling cuttings, we determined the pressure relaxation zone. Taking Guhanshan mining area as the object of study, we studied the pressure relaxation zone beside goafs of Guhanshan mining area using this method. The stress relaxation zone was determined by residual gas content and residual gas pressure, the dangerous parameters of outburst and the result of numerical simulation. The prediction results are 7-9m,8-10 m,null. Finally the stress relaxation zone is 8m in width by comprehensive analysis of all the results. |
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