掘进扰动下断层带煤体瓦斯异常分布特征研究

Study on abnormal distribution characteristics of coal gas in fault zone under tunneling disturbance

断层带的结构异性会导致介质渗透性的非均质性和各向异性,这对煤体内瓦斯渗流过程有重要影响。通过建立受掘进应力影响下的煤体渗透率模型和横向各向同性断层渗透率模型,利用COMSOL数值模拟软件对其进行解算分析,得出受断层影响的掘进工作面前方应力场及渗透率的演化特征规律。结果表明:受掘进应力影响,暴露面前方出现明显应力分带现象,塑性变形延续到距暴露面5 m处,且出现塑性区阶跃现象;考虑非均质断层的裂隙及煤基质瓦斯压力梯度分别为0.043、0.042 MPa/m,明显大于考虑均质断层的裂隙及煤基质瓦斯压力梯度,而且断层区域内渗透出现骤降及突增的现象,在断层核区域内渗透率降至最低为6.4383×10^(-18) m^(2),是煤层初始渗透率的1/7;断层影响区域瓦斯压力梯度大,透气性能低,验证了断层区域蕴育煤与瓦斯突出危险性高的合理性。

The structural heterogeneity of fault zone can lead to the heterogeneity and anisotropy of medium permeability,which has an important influence on the gas seepage process in coal.The coal permeability model and transverse isotropic fault permeability model under the influence of tunneling stress are established,and the COMSOL numerical simulation software is used to calculate and analyze it.The evolution characteristics of stress field and permeability in front of tunneling affected by faults are obtained.Theoretical and numerical simulation results show that:affected by tunneling stress,obvious stress zoning appeared in front of exposure surface,plastic deformation continued to 5 m away from exposure surface,and plastic zone step phenomenon appeared.The fracture and coal matrix gas pressure gradients considering heterogeneous faults are 0.043 MPa/m and 0.042 MPa/m,respectively,which are significantly higher than those considering homogeneous faults.In the fault core area,the permeability decreases to a minimum of 6.4383×10^(-18) m^(2),which is 1/7 of the initial permeability of coal seam.The large gas pressure gradient and low permeability in the fault-affected area verify the rationality of high risk of coal accumulation and gas outburst in the fault area.