A Study Of The Principles And Methods Of Quick Validation Of The Outburst-Prevention Effect In The Process Of Coal Uncovering

Coal and gas outburst is the worst disaster in the mining industry. With increasing exploitation depth, outburst under the condition of uncovering coal in crosscut is becoming more dangerous. Coal and gas outburst accidents occur frequently during the process of uncovering coal in deep mines. This is because inaccurate validation of the outburst-prevention effect leads to an outburst accidents. In fact, the validation of the outburst-prevention effect is the last outburst forecast before uncovering the coal seam, and the validation of the outburst-prevention effect is the main factor in determining whether the coal seam can be uncovered directly. Hence, the accurate validation of the outburst-prevention effect is a necessary method to ensure the safety of deep mine coal operations.Under the condition of coal uncovering in cross-cuts, if the outburst-prevention effect is taken and much gas drainage boreholes exist on the working surface, there are some deficiencies to use the original outburst prediction index validation of the outburst-prevention effect. Stratum are destroyed, the residual gas pressure is difficult to accurately measure. The prediction process is relatively complicated and long time. Some indicators are empirical and the critical value is poor universality. The static prediction coverage is small. Thus, it has important social and economic value to reduce harm of outburst, protecting workers’ life safety for study on methods for quick validation of the outburst-prevention effect in the process of coal uncovering.According to the change of coal seam after the outburst-prevention effect in the uncovering coal working face, a novel forecast indicator, which is the initial volume of gas emission from the borehole(IVGEB) was proposed to validate the outburst-prevention effect. First of all, theoretical basis of this method is researched and then COMSOL Multiphysics has been used to simulate gas emission characteristics from borehole under different conditions. Furthermore, the typical coal samples have been collected and after 100 test runs, the relationship between the IVGEB and gas pressure was obtained. Thus, based on the relationship of the initial expansion energy of released gas(IEERG) and gas pressure, the IVGEB critical value of weak outburst and intense outburst were obtained. The specific conclusions are as follows.(1) Gas flow model in the process of drilling was analysis and the gas seepage equation and analytical solution of gas emission from borehole were obtained. Then COMSOL Multiphysics has been used to simulate gas emission characteristics from borehole under different conditions.(2) A self-developed experimental device for measuring the initial rate of gas emission from the borehole(IRGEB) was developed which is consisted of the most advanced measuring element and technology. It could be continuous determination the IRGEB and its distribution at different times in the process of drilling, which realized the rapid determination of the IRGEB. Eleven coal samples under different coal types have been collected from the northwest, southwest, northeast, mid-east region of the main coal-producing provinces. After 100 test runs, the relationship between the IVGEB and gas pressure was obtained.(3) Analysis of the distribution curves of IRGEB, we found that IRGEB can reflect the coal seam outburst risk, no matter from long-flame coal, gas coal, coking coal and anthracite.(4) Borehole spraying is a kind of gas power phenomenon, belongs to a small outburst. The distribution curves of IRGEB when borehole spraying happened has been detected in the experiment successfully. The detected maximum IRGEB is 7.316L/s when borehole spraying happened from Henan Xuehu coal sample filled with CO2 under the pressures of 0.944 MPa. It is the average of 18 times.(5) To quantitatively describe an outburst-prone coal seam in the process of drilling, IVGEB has been taken as an index for validation of the outburst-prevention effect. IVGEB is the sum of the unit length of IRGEB, or the sum of the gas volume in a meter during the process of drilling. It found that the IVGEB value is approximately proportional to the gas pressure: the higher the gas pressure, the larger the IVGEB value. After determine IEERG of each coal sample, the results suggested that is the IEERG value approximately proportional to the IVGEB value. Based on the IEERG critical value of weak outburst and intense outburst were 42.98 m J/g and 103.8m J/g, the obtained IVGEB critical value of weak outburst and intense outburst were 44.65 L and 92.1 L. Outburst simulating test have been carried out to verify the IVGEB critical value of weak outburst and intense outburst prediction accuracy.(6) Due to the differentiation of the adsorption characteristics of coal, coal seam occurrence condition and geological conditions, the critical value of outburst will also be different. We should study the critical value of outburst every coal seam. When prediction the outburst danger of coal seam in the process of coal uncovering, we determine the original gas pressure of coal seam, IEERG and IVGEB. The relationship between IVGEB and gas pressure, the relationship between gas pressure and IEERG could be obtained. Thus, the IVGEB critical value of weak outburst and intense outburst for validation of the outburst-prevention effect in the process of coal uncovering could be obtained.