1. State Key Laboratory of High-efficiency Mining and Safety of Metal Mines,Ministry of Education,University of Science and Technology Beijing,Beijing　100083,China; 2. School of Civil and Resource Engineering,University of Science and Technology Beijing,Beijing　 100083,China; 3. China Coal Technology & Engineering Group Corp. ,Beijing　 100013,China

In order to explore the causes of unusual gas emission,coal and gas outbursts in coal mines with outburst elimination and traditional safe mining conditions during underground deep-mining process,the existence of low-gas catastrophes in gas-containing coal seams is confirmed by literature review and field investigation. Through field gas monitoring,microseismic observation and empirical analysis,the process and cause of low-gas catastrophes in the out- burst elimination of coal seams are recognized. Physical experiment and theoretical analysis on the gas-solid coupling of big coal samples with low-gas,the evolution path of stress-strain-seepage field at low-pressure and the physical catastrophe mechanism of gas-solid coupling for pressure-bearing coal samples are studied. There are many reports that the low-gas catastrophes in the coal seams can happen during mining process in deep coal mines with outburst elimina- tion and traditional safe mining conditions. Field observation and analysis reveal the model of low-gas catastrophes in coal seam under the action of roof weighting,roof weighting breaking impact and floor weighting impact. The boundary conditions of mining and excavation face are simulated,the catastrophic process at low-gas observed in the gas-solid coupling physical experiments at 0. 4 MPa pressure involves three steps: elastic compaction-gas constant velocity and deceleration steady seepage,plastic dilatation-gas growth unsteady seepage,and rupture instability-gas unsteady seep- age catastrophe. The conclusions are that many secondary fissures are formed in pressure stable area after taking out- burst prevention measures,which is beneficial for improving the de-sorption performance of gas. It could be the initial region of low gas pressure catastrophe,along with plenty of gas gathered. A “ three-zone” dynamic evolution theory of gas migration in front of mining-induced region of coal seams is given,and its characterization is clarified correspond- ing to the 40% extreme elasticity,and the ultimate failure load according to the change of stress value. In a word,the “three-zone” dynamic evolution theory of gas migration in front of mining-induced region of coal seams is the main reason of catastrophes with low-pressure gas. The catastrophic process and conditions for ordinary gas emission,unusual gas emission with low-gas,unusual gas emission with high-gas,and catastrophes are given. In addition,low-gas catas- trophes in gas-containing coal seams can be initiated in advance under the dynamic pressure impact of the superposi- tion of the roof and floor breakage.

国家自然科学基金资助项目(51674016，51274025，51534002)

LI Tie,PI Xiyu. Coupling catastrophes mechanism of low-gas in deep coal seams[ J]. Journal of China Coal Society, 2019,44(4):1107-1114.