远场应力作用下底抽巷对底板隔水性能影响及加固技术优化

Influence of roadway under coal seam floor on the water resistance of coal seam floor strata with far field stresses and the optimization of control technology

大水矿区底抽巷施工影响底板岩层隔水性能,增加煤炭开采的危险性并给底板注浆加固技术带来挑战。为此开展了远场应力作用下采动条件下底抽巷对关键岩层隔水性能影响及加固技术优化研究。根据底抽巷的轴向和断面特征,建立远场主地应力作用下底板关键岩层力学作用模型,求解有底抽巷和无底抽巷时底板破坏区下方粉砂岩的变形和弯矩理论解,进而研究底抽巷道条件下浆液充填套管在注浆加固岩层的应用效果,并进行数值验证。首先,根据研究区主要远场地主应力赋存特征得到局部坐标系中粉砂岩Ⅱ承受的应力分量σ′;然后根据弹性矩形薄板单三角级数的Levy解,运用广义简支边和叠加法,得到两邻边自由条件下工作面推采距离与工作面长度比分别为0.50、0.75、1.00、1.50和2.00时底板破坏区下方粉砂岩Ⅱ的变形和弯矩值。结果表明近似弹性条件下粉砂岩Ⅱ在底抽巷交叉点处的位移最大,且大于四边固支条件下同尺寸岩层最大位移;底抽巷影响下粉砂岩Ⅱ固定边承受的最大弯矩值比固支边时高一个数量级,同等条件下底抽巷使得粉砂岩Ⅱ更易发生变形,降低了粉砂岩Ⅱ抵抗变形性能和抗弯刚度。据此提出底板注浆加固工程优化方法,将浆液充填套管进入粉砂岩Ⅲ垂直深度2 m,给粉砂岩Ⅱ自由边增加约束,底板注浆加固工程中浆液充填长套管利用抗弯性能改善粉砂岩Ⅱ边界条件增加其抵抗强度,数值计算结果验证了底板注浆加固工程中浆液充填套管实际作用效果。

The construction of floor pumping roadway in flooding mining area can affect the water resistance of floor strata,increase the risk of coal mining and bring challenges to the floor grouting reinforcement technology.So,the study on the influence of roadway on the water resistance of floor strata under far field stresses and the optimization of control technology was carried out. According to the axial and cross section characteristics of the floor pumping roadway, an ana-lysis model of the bending resistance of key rock strata under the far field principal stresses was established and the theor-etical solutions of the deformation and the bending moment of the siltstone under the floor failure area with and without a floor pumping roadway were obtained. Furthermore, the application effect of grout filled casing pipes on the reinforce-ment of rock strata is studied and verified numerically. First, according to the far field principal stresses, the stress com-ponent σ′ acting on siltstone II is obtained in the local coordinate system. According to Levy solution of elastic rectangular thin plate single trigonometric series, the precise solutions of rock deformation and bending moment are obtained by using the generalized simply supported edge theory and superposition method. The exact solution of the deflection equation for the thin plate of strata penetrated by the gas roadway with two adjacent edges free and two adjacent edges fixed is got, while the ratio of mining distance to working face length is 0.50, 0.75, 1.00, 1.50 and 2.00, respectively. The calculation results show that the displacement of siltstone II at the intersection of roadway under the influence of roadway under the elastic condition is the largest, which is larger than the maximum displacement of the four sides fixed with the same geo-metric size. The maximum bending moment of the fixed side of siltstone II under the influence of floor pumping roadway is one order of magnitude higher than that of the fixed side. It illustrates that the siltstone II influenced by gas roadway is easier to be deformed than that without roadway, and its resistance to deformation is reduced to some extent. Based on this, an optimization method for grouting reinforcement of floor rock strata is proposed. The vertical depth of grout filling casing pipes entering into siltstone III is designed to be greater than 2 m, which can play the role of fixed end and increase constraints on free edge of siltstone II. The long slurry casing pipes can improve the boundary conditions of siltstone II and increase the resistance strength due to the deformation difference within the reinforcement range.The numerical res-ults verify the actual effect of grout filling casing on the siltstone deformation.