冲击载荷下含瓦斯煤动力学破坏特征与瓦斯渗流规律分析

Analysis of dynamic failure characteristics and gas seepage law of gas-bearing coal under impact loads

为探究不同冲击载荷和瓦斯压力作用下的含瓦斯煤动力学特征、裂隙扩展及瓦斯渗流变化规律,采用含瓦斯煤岩冲击损伤-渗流试验系统开展含瓦斯煤冲击试验以及原位渗流测试,并结合工业CT扫描系统进行试样裂隙结构的三维重构,分析含瓦斯煤内部裂隙扩展特征及其对瓦斯渗流的影响规律。研究结果表明,冲击载荷和瓦斯压力对含瓦斯煤的动力学性质、变形过程、裂隙扩展和渗流规律均具有重要影响,具体表现在:①受围压和轴压的影响,冲击载荷耦合瓦斯压力条件下的含瓦斯煤应力-应变曲线无明显压密阶段;含瓦斯煤的变形过程主要经历了弹性变形阶段、应变强化阶段及破坏阶段。②冲击载荷的增加对含瓦斯煤动力学参数具有强化作用,气体压力的升高则劣化了含瓦斯煤动力学参数;冲击载荷越大,瓦斯压力越高,含瓦斯煤的裂隙扩展愈充分,所形成的裂隙结构愈复杂。③含瓦斯煤的渗流规律受控于裂隙扩展,冲击载荷耦合瓦斯压力作用下,含瓦斯煤中存在孔隙流动、孔隙流动-裂隙流动并存及裂隙流动等3种气体流动形式;含瓦斯煤冲击破坏后,随着气体压力增加以及气楔作用的增强,瓦斯流动形式可由孔隙流动依次转变为孔隙流动-裂隙流动并存和裂隙流动;裂隙扩展和流动形式共同影响含瓦斯煤渗流规律,含瓦斯煤渗透率随瓦斯压力的增大总体上符合先增大后减小的变化趋势。

Using an impact damage-percolation experimental system for gas-bearing coal or rock,the authors carry out various gas-bearing coal impact experiments with in-situ seepage tests to reveal the law of dynamic mechanical characteristics,fracture expansion,and permeability changes of gas-bearing coal under different impact loads and gas pressures loading.Using an industrial CT scanning system,the authors conduct a 3D reconstruction of the fracture structure in order to analyze the internal fracture expansion characteristics of gas-bearing coal and the influence law on gas permeation patterns.The results show that both the impact load and gas pressure play an important role in the dynamic mechanical properties,deformation process,fracture expansion,and gas permeation patterns of gas-bearing coal:①Under the coupling of impact load and gas pressure,the stress-strain curve of gas-bearing coal has an inconspicuous compaction stage due to the influence of confining pressure and axial pressure.The deformation process of gas-bearing coal includes elastic deformation stage,strain strengthening stage,and failure stage.②The increase of impact load will increase the dynamic mechanical parameter value of gas-bearing coal,while the increase of gas pressure will reduce the value.The greater the impact load,the higher the gas pressure,and the more sufficient the fracture expansion of gas-bearing coal.At the same time,the fracture structure is more complex.③The seepage law of gas-bearing coal is controlled by fracture expansion.Under the coupling of impact load and gas pressure,three types of gas flow exist in gas-bearing coal:pore flow,coexistence of pore flow and fracture flow,and fracture flow.After the impact failure of gas-bearing coal,the gas flow pattern can transition from pore flow to coexistence of pore flow and fracture flow,and eventually to fracture flow,as the gas pressure increases and the influence of gas wedges intensifies.Fracture expansion and flow patterns jointly affect the seepage law of gasbearing coal.The permeability of gas-bearing coal generally exhibits a trend of initially increasing and then decreasing with the increase of gas pressure.