三轴应力作用下破碎煤体渗透特性演化规律

深部破碎煤岩体受地应力和开采扰动常处于三向应力状态,其渗透特性是影响矿井突水灾害预防和瓦斯抽放的重要因素之一。为研究深部破碎煤体的渗透性能,采用自主研发的破碎岩石三轴渗流试验系统,并设计一套破碎煤体三轴渗流试验方案,进行三轴应力作用下破碎煤体渗流试验,得到破碎煤体渗透特性随围压及孔隙率的演化规律。试验结果表明:①三轴应力作用下破碎煤样渗流雷诺数最大值为47. 58,渗流速度与孔压梯度两者之间符合Forchheimer关系;②三轴应力作用下破碎煤样的孔隙率与围压的变化规律呈负相关,各级轴向位移下,两者服从对数函数关系;③随着有效应力的增大,各粒径下的破碎煤样孔隙率逐渐减小,破碎煤样孔隙率的理论计算值与试验结果较为吻合,表明文中给出的孔隙率计算方法可行;④各级轴向位移下,破碎煤样的渗透率随围压增大而减小,不同粒径的破碎煤样渗透率随围压的演化规律可用k=me^nσ3公式表示,颗粒粒径越大,破碎煤样的渗透率随围压的变化越敏感;⑤颗粒粒径及孔隙排列方式影响破碎煤样渗透性能,不同粒径破碎煤样随孔隙率的减小,渗透率整体减小,非Darcy流β因子呈增大趋势,其中渗透率的量级为10^-14～10^-10 m^2,非Darcy流β因子的量级为10~7～10¹¹m^-1。所得研究结论有助于增强深部破碎煤岩体渗透特性演化规律的认识。

Permeability evolution of broken coal under triaxial stress

The deep broken coal and rock mass are often in the state of triaxial stress,due to the crustal stress and mining disturbance,and its permeability is one of the important factors that affect the prevention of mine water inrush disaster and gas drainage.This research aims to carry out the seepage test of broken coal under the triaxial stress,using the self developed triaxial permeability test system for broken rocks,and the evolution law of the permeability characteristics of the broken coal with the confining pressure and the porosity are obtained.The results are as follows ① the maximum Reynolds number in fluid flow through broken coal under triaxial stress is 47.58,and the seepage velocity and pore pressure gradient are fitted by the Forchheimer relationship.② Under triaxial stress,there is a negative correlation between the porosity and confining pressure of broken coal,and both agree with the logarithmic function relationship.③ The theory of broken coal porosity values are close to the experimental results,and the porosity decreases with the increase of the effective stress.Thus it shows that the calculation method of porosity is feasible.④ Under the axial displacement at all levels,the permeability of broken coal decreases with the increase of confining pressure,and the evolution law of permeability of broken coal with different diameter sizes with confining pressure can be expressed by formula k=menσ3.The larger the particle size,the more sensitive the permeability of the broken coal changes with the confining pressure.⑤ The permeability of broken coal is affected by particle size and pore arrangement.With the decrease of porosity,the permeability of the broken coal in different diameter sizes are on the downward trend,and non Darcy flow β factor increases,integrally.The order of the permeability is 10-14-10-10 m2;the order of non Darcy flow β factor is 107-1011 m-1.The results will be helpful to the understanding of permeability evolution of broken coal and rock mass.