增透抽采瓦斯煤岩体裂隙演化及蠕变失稳机理研究

From low-permeability coal seams, the coal rocks around the working face of permeability-increasing gas extraction are colleted and the structure of cracks of these coal rock samples is analyzed by electronic microscope scanning, CT scanning and analytical experiment of micro-porous structure.The mechanical properties and seepage characteristics of creeping coal rock samples are obtained by the MTS815 testing machine through which the strength, creep strain and seepage tests are done.The sound signals and the full-field strain of the sample surface during the deformation process of coal rock samples are obtained by the use of sound emitter and a non-contact full-field strain measuring system.The whole process of gas extraction from creeping coal rocks is simulated by a 3-D coal mining simulating experimental platform. At worksites, gas density and flow rate are monitored and the cracks and stress of coal rocks are observed. Meanwhile, the relationships between Crack evolution law in coal rocks and their creepage characteristics are studied and the newly formed structures are also studied. Based on these studies, a coupling mathematic model is established for the stress field and gas seepage field of creeping coal rocks and crack evolution equations and the creeping instability model of coal rocks are also formulated respectively through the comprehensive application of damage fracture mechanics, seepage mechanics, rheology mechanics, and catastrophe theory. Furthermore, numerical simulation calculation and analysis for the above-mentioned equations and models are done to reveal the mechanisms of coal rock crack evolution and creeping instability of low permeability coal seams during gas extraction. Finally, theoretic foundation to extract gas safely and effectively is laid.

针对低透气性煤层瓦斯增透抽采工作面周围煤岩体，通过电镜扫描、CT扫描和微孔结构分析实验研究其微观孔裂隙结构；利用MTS815试验机进行煤岩样强度、蠕变变形和渗流试验，获取蠕变煤岩样力学特性和渗透特性；采用声发射仪和非接触式全场应变测量系统获取煤岩样变形过程的声发射信号及其表面全场应变；利用三维含瓦斯煤开采物理相似材料模拟实验平台模拟蠕变煤岩体内瓦斯增透抽采全过程，观测煤岩体钻孔周围应力变化及其裂隙演化过程，测取瓦斯浓度及流量变化，获取煤岩体内裂隙演化和蠕变变形规律及其与瓦斯渗流间的关系。在此基础上，综合运用损伤断裂力学、渗流力学、蠕变力学、突变理论，分别建立蠕变煤岩体的应力场和瓦斯渗流场耦合数学模型，裂隙演化方程和煤岩体蠕变失稳模型，并对以上模型方程进行数值解算和分析，从而揭示低透气性煤层增透抽采过程中煤岩体裂隙演化及其蠕变失稳机理，为采掘过程中瓦斯安全高效抽采提供理论依据。

本项目针对瓦斯抽采增透措施中存在的问题，以煤岩体裂隙演化及其蠕变失稳机理为研究主线，综合运用损伤断裂力学，渗流力学，蠕变力学，突变理论，采用数值模拟计算，室内试验及现场监测分析相结合的方法，进行了大量科学研究，取得了如下的主要成果：获得了蠕变煤岩体的渗流及力学参数，得到了蠕变作用对煤岩体渗流的影响规律，建立了煤岩体流固耦合动力学模型。获取了钻孔孔周煤岩体裂隙演化规律，建立了采动影响下的抽采钻孔孔周裂隙扩展模型，并得到了采掘活动对覆岩裂隙演化的影响，揭示了煤岩体损伤及裂隙演化机理。最后，考虑深部矿井的复杂力学条件，分析煤岩体蠕变失稳条件，建立了非线性大变形蠕变失稳模型，揭示了深部矿井巷道围岩变形机制，并针对性地提出了解决措施，为井下绿色、安全生产和瓦斯高效抽采提供科学依据。