不同初始瓦斯压力下煤体动力学特性及其劣化特征

Dynamic behaviors and deterioration characteristics of coal under different initial gas pressures

为探究不同初始瓦斯压力下煤体动力学特性及其劣化规律,利用自主研发的含瓦斯煤岩动静组合加载试验系统对含瓦斯煤开展冲击压缩试验,结合CT扫描系统分析了含瓦斯煤内部裂隙的扩展演化规律,并基于不同初始瓦斯压力下冲击煤样内部裂隙率增量定量表征了其细观损伤程度,探讨了冲击荷载作用下含瓦斯煤宏观力学参量劣化规律。研究结果表明:(1)冲击荷载作用下含瓦斯煤动态应力-应变曲线无明显压密阶段,分为线弹性阶段、塑性硬化阶段和破坏阶段,并发现随初始瓦斯压力升高,冲击煤样峰值强度、峰值应变和弹性模量均出现弱化现象;(2)瓦斯加剧了煤体内部裂隙的扩展和贯通,并根据CT扫描结果发现,含瓦斯煤冲击破坏模式主要以劈裂和层裂破坏为主,随初始瓦斯压力升高,两种破坏模式越显著,煤体内部裂隙数量及其损伤程度逐渐增大,空间裂隙网络更为复杂;(3)基于细观层面定义了损伤变量,得其值随初始瓦斯压力升高呈现二次函数上升,对比冲击载荷作用下煤体动态强度与以裂隙率增量定义损伤程度所得理论强度,验证了细观层面煤体裂隙率增量定义损伤变量的合理性,建立了含瓦斯煤细观劣化与宏观参量损失的内在联系。研究成果丰富了含瓦斯煤动力学基础理论,为矿井煤岩瓦斯复合动力灾害的防治提供了理论参考。

In order to investigate the dynamic behaviors of coal and its deterioration law under different initial gas pressures, this study conducted impact compression experiments on gas-bearing coal by using the self-developed visualized gas-bearing coal rock dynamic and static combined loading test system, analyzed the expansion and evolution law of internal fracture in gas-bearing coal by combining with CT scanning system. Moreover, this study also quantitatively characterized the mesoscopic damage degree based on the increment of internal fracture rate of coal samples impacted under different initial gas pressures, and explored the deterioration law of macroscopic mechanical parameters of gas-bearing coal under the impact load. Some conclusions are drawn.(1) The dynamic stress-strain curves of gas-bearing coal under impact loading, which can be divided into linear elastic phase, plastic hardening phase and damage phase, have no obvious compaction phase. And it is found that the peak strength, peak strain and elastic modulus of impacted coal samples deteriorate with the increase of initial gas pressure.(2) Gas aggravates the expansion and coalescence of fractures inside the coal. CT scanning results indicate that the impact damage mode of gas-bearing coal is mainly splitting and stratified splitting damages, and the more significant the two damage modes are with the increase of initial gas pressure, so does the number of fractures and their damage degree inside the coal, which makes the spatial fracture network more complex.(3) The damage variables are defined on a mesoscopic level, and the values of damage variables show a rise of quadratic function with the increase of initial gas pressure. The comparison of the dynamic strength of coal under impact load with the theoretical strength obtained by defining the degree of damage by fracture rate increment verified the rationality of the damage variables defined by fracture rate increment of coal at the mesoscopic level. The intrinsic connection was constructed between the mesoscopic deterioration of gas-bearing coal and the loss of macroscopic parameters. The research results enrich the basic theory of gas-bearing coal dynamics and provide a theoretical reference for the prevention and control of coal-rock-gas composite dynamical hazards in mines.