基于逾渗机理的含瓦斯煤体变形破坏机制及试验研究

Deformation failure mechanism and experimental study of gas-bearing coal rock mass based on percolation mechanism

针对含瓦斯煤岩在高应力环境下易发生松散破坏的问题,考虑煤体的多孔介质特征,研究了含瓦斯煤岩受应力扰动影响下的变形破坏规律。首先,基于逾渗理论提出了含瓦斯煤体的逾渗破坏概念,它的实质是含瓦斯煤岩发生逾渗行为后导致瓦斯突出使煤体失稳破坏过程中发生的一种动力破坏现象。然后通过理论分析了逾渗破坏分布区域并给出了逾渗破坏概率P_∞的计算公式,推导出了含瓦斯煤体的Biot型本构方程,表明含瓦斯煤体孔隙率与渗透系数和有效应力密切相关。结合含瓦斯煤体本构方程并在逾渗破坏区进行了应用,得到了逾渗破坏区半径R_p的计算公式。最后,对拟制备的含气类岩石试件进行了三轴压缩试验,试验结果表明:随着试件孔隙、裂隙增多,弹性模量和脆-延性破坏临界拐点应力值随之减小;同时,黏聚力和内摩擦角值随试件内部气体孔隙增加均不同程度的降低,导致逾渗破坏区半径增大,并且其影响程度会随内摩擦角和黏聚力的减小而增强。随着应力增加,试件内部孔隙、裂隙逐渐贯通,最终呈松散破坏即逾渗破坏。

Aiming at the problem of loose damage caused by gas in high stress environment and taking into account the porous media characteristics of coal and rock mass,the failure deformation mechanism under the influence of stress disturbance of gas-bearing coal and rock mass was studied.Firstly,the concept of gas-bearing coal and rock mass percolation failure was put forward based on percolation theory,whose essence is a kind of dynamic failure which occurs when the gas is protruded to cause the coal rock to break down.Then,the distribution area of percolation damage was analyzed and the calculation formula of percolation failure probability P∞ was given.The Biot-type constitutive equation and field equation of gas-bearing coal rock mass are deduced by classical mixture theory.The results show that the pore and fracture of gas-bearing coal and rock mass are closely related to permeability coefficient and effective stress.Finally,according to the constitutive equation of gas-bearing coal,the method was applied to the percolation failure zone,and the formula of percolation damage zone radius Rpwas obtained.Based on the preparation of the rock specimen containing gas of three axial compression test,the test results show that with the increase of the pores and fissuresof the rock specimen,the specimen elastic modulus and the brittle-ductility critical failure point decrease.At the same time,specimen cohesion and internal friction angle values were reduced in different degrees with the increase of internal gas pore,resulting in increased percolation damage zone radius,and its influence will enhance with the decrease angle of internal friction and cohesion.Finally,with the increase of stress,the pore pressure increases,when the stress continues to increase,the pores and fissures gradually pass through,and the specimens eventually undergo loose failure,that is percolation damage.