承压煤岩低气压渗流灾变

Low gas pressure seepage and catastrophe of pressurized coal

摘要:

为探索含低压瓦斯煤层的瓦斯异常涌出灾变成因与机理,对目前该领域的文献进行了分析与总结,并通过工程案例实证分析,证明了此种灾变的存在；在流固耦合实验系统上,按背景工程约束与加载条件开展含低气压煤样承压物理试验,得到了灾变全程应力-声发射-流量实验数据及试样外表破坏情况；用UDEC,按背景工程边界与加载条件开展气-固耦合离散元数值试验,得到了灾变全程应力-应变--流速-位移速率等实验数据及试样内部破裂情况.研究结果表明:3种研究方法获得了一致性较高的结果,0.4 MPa气体压力下,煤层承压过程应力-煤-气耦合作用,可以导致发生喷出气体的灾变,在煤矿现场多表现为瓦斯异常涌出超限；在单自由度边界条件下施加单向压载,承压煤岩弹性变形前期,气体沿原生裂隙和孔隙呈常速稳态渗流；弹性变形后期,原生裂隙和孔隙被压密,气体呈减速稳态渗流；屈服阶段,扩容新生裂隙产生,气体呈加速非稳态渗流；达到极限荷载或峰后不久,发生气体喷出灾变；采、掘作业面正常通风条件下,气流瓦斯浓度持续降低,是煤层发生瓦斯异常涌出的警示信息,应引起高度重视.

Abstract:

To explore the cause and mechanism of the disaster caused by abnormal gas emission in coal seams with low-pressure gas, the literature in this field was analyzed and summarized, and the existence of such disaster was verified by case study. Based on the fluid-solid coupling experimental system, the physical test of coal sample bearing pressure with low pressure was carried out according to the constraints and loading conditions of the engineering, and the overall stress-acoustic emission-flow experimental data and the external damage of the sample were obtained. Using UDEC software, the discrete element numerical experiments of gas-solid coupling were carried out according to the boundaries and loading conditions of the engineering, and experimental data such as stress-strain-displacement rate and internal cracking of the sample were gained. Results show that the three methods had a high consistency. With the gas pressure of 0.4 MPa, gas outburst occurred under stress-coal-gas coupling, and it generally appeared as the amount of gas emission exceeding the limit in coal mine. The unidirectional pressure load was applied under the single-degree-of-freedom boundary condition. At the early stage of the elastic deformation of the pressure-bearing coal rock, the gas flowed along initial cracks and pores at a normal steady speed. At the later stage of the elastic deformation, the initial cracks and pores were compacted and gas flowed at a slow steady speed. During the yield phase, the new fissures triggered by coal dilatancy were formed and gas flowed rapidly and unsteadily. When the coal mass bore approximately achieved ultimate load or shortly reached the peak, gas outburst disaster happened. The phenomenon of continuous decrease of gas concentration faced in the mining and excavating work under normal ventilation is a warning sign that coal seams have abnormal gas emission, and to which great importance should be attached.