Experiment Study On Method Of Initial Gas Emission From Borehole(IGEB) For Outburst Prediction In Cross-cut Coal Uncovering

Compared with the other type outbursts, occurrence of intense outburst in cross-cut coal uncovering brings great disaster to the mine seriously threating the safe in coal production. The size is bigger and bigger as mining is extended deeper. Study on methods for outburst prediction in cross-cut coal uncovering has significant and practical meaning for coal mines safety production. From the view of mine application, some current methods play a certain role in solving the problem but there are some shortcomings, such as insensitive indexes, limited boreholes for gas pressure determination, relatively complicated process and long time and low accuracy of gas pressure determination. Therefore, it is necessary to study a new mothod for outburst prediction in cross-cut coal uncovering.In this paper, Xuehu, Fenghui, Wangchao, Wuzhong, Yiluo coal samples are taken as the research object. The mothod of initial gas emission from borehole(IGEB) is proposed based on theoretical analysis and experimental research. First of all, theoretical basis of this method is researched, and then sample data of IGEB are collected in many experiments, at last index threshold is obtained by discriminant analysis method. The main conclusions of this paper are as follows.(1) A device for IGEB determination is developed which is consisted of the equipment for obround coal seam simulation and the equipment for gas flow testing, and 50 groups of IGEB data are measured in drilling with diameter of 42 mm and distance of 1 m, in which 48 data are effective and the other 2 data are invalid caused by intense orifice phenomenon during drilling.(2) Relationship between IGEB and gas pressue and gas type is found. For the same coal seam, IGEB increases with gas pressure. At the same pressure, value of the index under CO2 condition is larger than that under N2 condition. According to the two relations, it is concluded that the index of IGEB can well reflect the outburst danger.(3) Outburst-prone coal is identified by measuring the expansion energy of initial released gas(EEIRG) under the condition of IGEB determination.(4) Research shows that there is a big difference between the IGEB value of non-outburst coal seam and that of outburst-prone coal seam which indicates that IGEB is a sensitive index to non-outburst and outburst coal seams.(5) The index with a fixed threshold can be well applied in the coal seam classification under CO2 and N2 conditions simultaneously. Thus, we think that the index with the same threshold can be also applied to the coal seam containing CH4 gas.(6) Discriminant analysis method is applied to process the data of IGEB, and the thresholds for weak outbursts and intense outbursts are obtained, they are 36.63 L and 80.85 L, respectively. Accurate returned classification rates are 94.74% for non-outbursts and weak outbursts, and 92.86% for weak outbursts and intense outbursts, which indicates that the obtained thresholds are of highly reliable.(7) Eight outburst simulation results are consistent with the outburst prediction results by IGEB mothod, which verifies this method is suitable for outburst prediction in cross-cut coal uncovering.