深部承压水上含隐伏构造煤层底板渗流路径扩展规律

针对邯邢矿区矿井开采深度逐渐加深与采动影响下隐伏构造活化而导致底板奥灰层突水威胁日益加重的问题,研究大采深、高水压条件下含不同隐伏构造类型底板高承压水的始渗条件和渗流路径扩展规律,以确定矿井底板突水条件及重点治理区域。从开采扰动、隐伏构造、承压水共同作用角度分析,根据典型突水矿井地质条件及突水原因分析,建立了含隐伏导含水构造的概化力学模型,通过断裂力学理论得出了含水裂隙的起裂条件、抗渗透强度及由主应力表达的裂隙扩展判据,应用弹性力学边界荷载在半无限板内传播的经典求解方法推导得出了采动应力与承压水压力耦合作用下含隐伏构造煤层底板的垂直应力、水平应力和剪切应力表达式,在所得应力分量基础上通过应力张量的不变量求解应力状态方程得到含水裂隙扩展判据中的主应力表达式,以邯邢矿区典型突水矿区地质与开采参数为例进行算例分析,通过编制Matlab计算程序计算得出底板裂隙的扩展路径。进而采用可模拟岩石破裂声发射且裂隙扩展可视化效果较好的RFPA数值软件进行验证分析,再现了底板渗流路径演化过程。理论计算与数值分析结果表明:隐伏构造的局部应力扰动作用影响了渗流路径的扩展方向,使3种类型底板分别呈现出不同的渗流路径,对于完整型底板,渗流裂隙由奥灰承压水层顶界面至采空区两侧边界呈"正八字"形向采空区扩展;对于隐伏陷落柱型底板,渗流裂隙沿陷落柱顶界面呈"倒八字"形向上发散式扩,至底板28 m深度时与采动裂隙贯通而停止扩展,其延线分别指向采空区两侧边界展;而对于隐伏断层型底板,渗流裂隙则沿断层延线的反向扩展,至底板30 m深度时与采动裂隙贯通而停止扩展,其延线指向工作面后方,在底板含水裂隙自下而上与底板采动裂隙自上而下联合扩展作用下最终贯通形成底板奥灰水至采煤工作面的渗流通道。基于理论计算和数值模拟得出的底板承压水渗流路径扩展规律,在实际工程中可结合微震监测技术来实时动态捕捉煤层底板隐伏导含水构造活化的前兆信息,进而实现底板突水路径的预测预报和快速重点区域治理。

Expansion law of seepage path in the concealed structural floor of coal seam in deep confined water

With the mining depth gradually increases,the coal mines in Hanxing mining area are facing an increasing serious problem of water inrush threat from the ordovician limestone caused by the activation of concealed structures under the influence of mining.In order to determine the water inrush condition and the key treatment areas of coal seam floor,the initial seepage conditions and seepage path expansion laws of high confined water with different concealed structural types under the conditions of large deep and high water pressure should be studied.Therefore,the generalized mechanics models were established from the coaction mechanism of mining disturbance,concealed structure,combination of confined water,based on the analysis of geological characteristics and water inrush of typical coal mines in Hanxing mining area.According to the generalized mechanics models,the cracking condition,seepage strength and water-crack expansion criterion expressed by the principal stresses were obtained by the theoretical analysis of fracture mechanics.Then a classical solution method of boundary loads propagation in semi-infinite elastic plates was applied to derivate the mathematical expressions of the vertical,horizontal and shear stresses of the concealed structural coal seam floor under the coupling of mining stress and confined water pressure.Based on the obtained stress components,the stress state equation was solved by the invariants of the stress tensor to obtain the principal stress expression in the above water-crack expansion criterion.Taking the geological and mining parameters of the typical water inrush mine area in Hanxing area as an example,the case study was carried out and the extended path of coal seam floor crack was calculated using the Matlab program.Furthermore,the RFPA numerical simulation software,which can effectively simulate rock rupture and make fracture extension process visual,was applied to analyze the mechanical behavior of floor with different types of concealed structure and reconstruct the evolution process of confined water seepage path.The results of theoretical calculation and numerical analysis showed that the local stress disturbance of the concealed structure affected the expansion direction of the seepage path,so that three types of coal seam floor respectively showed different seepage paths.For the intact type of coal seam floor,the seepage crack extended to the boundary of both sides of the goaf with a “positive eight-character” shape from ordovician confined water layer.For the coal seam floor with concealed collapsed column,the seepage crack extended to the boundary of both sides of the goaf with an “inverted eight-character” shape from the top interface of the collapsed column to the depth of 28 m.For the coal seam floor with concealed fault,the seepage crack extended along the opposite direction of the fault extension line and stopped at depth of 30 m.The floor water-bearing fracture and the mining fracture expanded to each other and finally formed a seepage channel from ordovician confined water layer to the coal mining face.The result of seepage crack extension law of coal floor with different types of concealed structure obtained by theoretical analysis and numerical simulation could be used for predicting the confined water inrush path and targeted treatment of ordovician limestone kaster water disaster,in combination with microseismic monitoring technology which real-timely and dynamically catch the precursor information on concealed structure activation.