夹矸影响下的含瓦斯煤裂隙演化规律探究

Exploration of the Evolution Law of Gas-containing Coal Fissure under the Influence of the Gangue

  • 摘要: 为探究夹矸影响下的含瓦斯煤的裂隙演化规律,本文以含瓦斯煤为研究对象,利用受载煤岩工业CT扫描系统,设计开展了恒定围压、不同瓦斯气压加载破坏的不同夹矸厚度、不同夹矸层数的受载含瓦斯煤裂隙扫描实验,获取了多种含瓦斯煤裂隙原始CT图像,通过三维重构技术得到了含瓦斯煤的数字化模型,实现了含瓦斯煤内部裂隙空间结构的可视化,并运用Avizo软件计算结构参数,对含瓦斯煤裂隙演变特性进行定量分析。研究结果表明:含瓦斯煤试样三轴加载的破坏形式为剪切破坏,纯煤试样裂隙呈现出平行、交叉等复合型式;夹矸试样裂隙主要集中于煤体部分,只有一两条主要裂隙延伸至岩体部分并扩展贯穿夹矸层,夹矸层受损程度较小;双层夹矸试样损伤主要集中于两层夹矸之间的煤体部分,破裂后的宏观裂纹多表现为“A”字形的特征;夹矸影响下的含瓦斯煤破裂后的裂隙率、三维分形维数与平均配位数随瓦斯压力的增加而增加,裂隙率、三维分形维数、平均配位数随夹矸厚度、夹矸层数增加而降低;瓦斯压力的增加导致库伦破坏线与莫尔应力圆互相接近,逐渐接近试样的破坏条件,促使裂隙更加容易发育;夹矸厚度的增加,降低了裂纹扩展能量释放率,临界裂隙长度增大,裂隙扩展更难发生。

     

    Abstract: To investigate the crack evolution of gas-bearing coal under the influence of interburden, this study focuses on gas-bearing coal as the research object. Using an industrial CT scanning system for coal-rock under load, a series of experiments were designed and conducted under constant confining pressure, with different gas pressures and varying interburden thickness and number of layers. These experiments were used to scan the cracks in gas-bearing coal under load, obtaining original CT images of the cracks in gas-bearing coal. Three-dimensional reconstruction techniques were employed to create digital models of the gas-bearing coal, allowing for visualization of the internal crack structure. The structural parameters were then calculated using Avizo software for quantitative analysis of the crack evolution characteristics in gas-bearing coal. The results indicate that the failure mode of gas-bearing coal samples under triaxial loading is shear failure. The cracks in pure coal samples exhibit composite forms such as parallel and intersecting cracks. In interburden coal samples, cracks mainly concentrate in the coal body, with only one or two major cracks extending into the rock mass and penetrating the interburden layer, which shows little damage. In the case of double-layer interburden samples, damage is primarily concentrated in the coal body between the two interburden layers, and the macro-cracks after failure typically exhibit a characteristic "A"-shaped pattern. Under the influence of interburden, the crack ratio, three-dimensional fractal dimension, and average coordination number in gas-bearing coal increase with the increase in gas pressure, while these parameters decrease as the interburden thickness and number of interburden layers increase. The increase in gas pressure causes the Coulomb failure line and the Mohr stress circle to approach each other. Gradually, the conditions for sample failure are approximated, facilitating the development of fractures more easily. The increase in interburden thickness reduces the energy release rate of crack propagation, increases the critical crack length, and makes crack propagation more difficult.

     

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