不同应力路径下两种典型煤样瓦斯渗透性研究

Research of Gas Permeability of Two Typical Coal Samples Under Different Stress Paths

瓦斯渗透率是影响瓦斯抽采效果的重要参数.针对原生结构煤与构造煤两种典型煤样分别进行了常规三轴压缩及增轴压卸围压两种应力路径下的瓦斯渗透性测试,结果表明:构造煤煤样变形能力较大,在常规三轴加载及增轴压卸围压两种应力路径下,应变-渗透率曲线变化较为缓和,在峰值应力后出现反转,但增加速率较小.构造煤结构在载荷下的颗粒重组及裂隙揉搓封闭是导致其渗透性变化的主要原因.原生结构煤强度大,变形能力弱,应变-渗透率在屈服应力处出现反转,渗透率猛增.对比两种应力路径发现,增轴压卸围压路径下,渗透率变化更为剧烈,在屈服应力处渗透率增加速率变大,峰值应力处,达到最大值.结合声发射特征,得到了原生结构煤裂隙萌生、发展及贯通的宏观破坏特征是瓦斯渗透性出现渗流突变的主要原因.从构造煤与原生结构煤的对比情况可以发现,渗透率与变形之间并不是一致性关系,构造煤变形大,但渗透率变化较为缓和,原生结构煤变形小,渗透性出现急增现象.同时,应力路径对于构造煤瓦斯渗透性影响较小,对原生结构煤影响较大.

Gas permeability is an important parameter influencing gas extraction effect. A test was carried out in which the gas permeability of the typical coal samples of primary structural coal and tectonic coal was determined under two different stress paths-the conventional triaxial compression, on the one hand, and increasing axial pressure and unloading confining pressure, on the other. The results indicated that the tectonic coal samples had larger deformation capacity. Its strain-permeability curve showed but a slight change under the two kinds of stress path. A reversal appeared after peak stress, but the increasing rate was rather small. Particle reorganization and fissure kneading closure of tectonic coal structure under load were shown to be the major cause leading to its permeability change. Primary structural coal had bigger strength than tectonic coal, its deformation ability was weak, and a reversal occurred at the yield stress in strain, resulting in a sharp rise in permeability. Comparing the two kinds of stress path, it was found that permeability change was more intense under the path of unloading confining pressure and increasing axial pressure, and permeability increased faster at yield stress and reached the maximum at peak stress. Based on the features of acoustic emission, crack initiation and development and the macroscopic failure characteristics of primary structural coal were the main causes for gas permeability in seepage mutations. A comparison of tectonic coal and primary structural coal suggested that the relationship between permeability and deformation was not consistent. Deformation of tectonic coal was large, but the permeability change was moderate, while the deformation of primary structural coal was weak, but its permeability increased sharply. At the same time, the stress path had greater effect on the gas permeability of primary structural coal than on that of the tectonic coal samples.