煤矿采空区岩体渗透性计算模型及其数值模拟分析

煤矿采空区岩体渗透性是煤矿采空区煤层气抽采设计的基本参数。从煤矿采空区岩体变形-破坏特征分析入手,通过理论分析研究了岩体渗透性与应力之间的耦合关系和模型,揭示了采空区岩体应力-应变和渗透性分布规律。研究结果表明:不同岩性岩石的渗透性在全应力-应变过程中为应变的函数,采空区岩体渗透性决定于岩体破坏程度和断裂的张开度,基于采空区岩体应力-应变导致断裂开度变化,推导了采空区岩体渗透系数与应力之间的三维关系与模型;应用FLAC~(3D)计算软件,对采空区岩体应力-应变-渗透性进行了数值模拟计算,分析了采空区岩体的变形破坏的分区分带特征,在纵向上自上而下形成弯曲下沉带、断裂带和垮落带;在横向上划分为原岩应力区、超前压力压缩区、卸载应力区和岩体应力恢复区;揭示了采空区岩体渗透性分布与采空区岩体应力-应变和破坏规律相一致的特征。无论是垂直渗透系数比(K_z/K_(z0)),还是水平渗透系数比(K_y/K_(y0)),均随着距开采煤层垂直距离的增大,采空区岩体渗透性逐渐减小,且采空区边缘的渗透系数较大,采空区两侧煤柱区岩体渗透性显著降低。

Calculation model of rock mass permeability in coal mine goaf and its numerical simulation analysis

Permeability of rock mass is a basic parameter of CBM extraction design in coal mine goaf.Starting from the analysis of deformation and failure characteristics of rock mass in coal mine goaf，through theoretical analysis，the coupling relationship and model between the permeability and stress of rock mass was studied，then the distribution regularity of stress，strain and permeability in the coal goaf was revealed.Research results show that the permeability of different lithology rocks is considered as a function of strain in the stress-strain process，which depends on both the damage degree and the openness of fracture.Based on the openness of fracture caused by the stress-strain of rock mass in the goaf，the three dimensional relationship and model between the permeability and stress was deduced.Using the calculation software FLAC3D，the simulated calculation was carried out in the stress-strain-permeability of rock mass in the goaf，the segmental characteristics of the deformation and failure of rock mass in the goaf was analyzed，which was formed into the bending subsidence zone，fractured zone and carving zone from top to bottom in the vertical direction and divided into the original in-situ stress area，abutment pressure compression area，unloading stress area and recovery area in the horizontal direction.The characteristics of the permeability distribution which is consistent with the stress-strain and failure law was revealed.Both the coefficient ratio of vertical permeability ( Kz/Kz0 ) and that of horizontal permeability ( Ky/Ky0 ) increase with the increase of the vertical distance from mining coal seam，the permeability of rock mass in the goaf gradually decreases，and the permeability coefficient on the edge of the goaf is larger，while the permeability on both sides of the coal pillar zone decreases significantly.