深部煤层低瓦斯耦合灾变机制

为探索深部开采中消突并达到安全开采条件煤层发生瓦斯异常涌出或煤与瓦斯突出的成因,通过文献调研和现场调查,确认含瓦斯煤层低压灾变的存在;通过现场瓦斯监测、微震观测、实证分析,认识消突煤层低瓦斯灾变的过程与成因;通过含低气压大煤样气-固耦合物理试验和理论分析,研究承压煤样低气压应力-应变-渗流场演化路径和气-固耦合物理灾变机制。结果显示,进入深部开采后陆续有消突达到安全开采条件煤层发生低瓦斯灾变现象的报道;现场观测和分析揭示出顶板来压、顶板来压破断冲击和底板来压起臌冲击作用下煤层低瓦斯灾变的模式;模拟采、掘工作面边界条件,0.4 MPa气压条件下的气-固耦合物理试验观察到了低气压灾变过程的3个阶段:弹性压密——气体常速与减速稳态渗流、塑性扩容——气体增速非稳态渗流、破裂失稳——气体非稳态渗流灾变。得到:在防突措施扰动下,稳压区煤层已不再是原生状态裂隙,而有大量新生裂隙产生,为瓦斯解吸游离创造条件,可形成局部富集区,是瓦斯低压灾变的发动区;分析得出采动超前区段瓦斯赋存状态"三带"动态演化规律,根据峰值应力,定量划分出40%极限弹性、极限弹性和极限破坏载荷所对应的"三带"动态演化特征;采动瓦斯赋存"三带"动态演化是导致低压瓦斯灾变的主要原因;提出了瓦斯普通涌出-低值异常涌出-高值异常涌出的灾变过程和条件;顶、底板破断冲击动压叠加作用下,可导致含瓦斯煤层低压灾变提前发动。

Coupling catastrophes mechanism of low gas in deep coal seams

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 outburst 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 elimination 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 seepage catastrophe.The conclusions are that many secondary fissures are formed in pressure stable area after taking outburst 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 corresponding 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 catastrophes in gas containing coal seams can be initiated in advance under the dynamic pressure impact of the superposition of the roof and floor breakage.