深部近距离煤层群采动力学行为探索

我国深部近距离煤层群赋存开采比重大,采动力学机理不清,导致开采效率低,安全事故频发。深部煤岩体所表现出的物理力学特性及变形破坏特征较浅部有着本质差异,尤其在深部近距离煤层群开采条件下,临近工作面扰动影响将导致更加复杂的采动应力重分布过程。针对深部近距离煤层群采动影响下巷道围岩控制难题,依托平煤十二矿己_(14)和己_(15)深部近距离煤层群工程实践,在己_(15)-31030工作面进风巷内开展了巷道收敛变形、锚索应力现场原位监测试验,理论计算了近距离煤层群底板破坏范围并推导得出了巷道围岩变形速度公式,初步揭示了深部近距离煤层群采动力学行为。研究表明:己_(14)煤层底板破坏深度理论值约21.24～30.88 m,上覆煤层采动影响导致本煤层采场边界改变,巷道顶底板及左右帮收敛量约400 mm,巷道收敛变形量随采煤工作面推进呈现阶梯式缓慢增长与指数式快速增长两阶段模式,其中指数式快速增长阶段为巷道变形的主要阶段;锚索应力随采煤工作面推进呈现"近线性增长—跃阶式降低"两阶段演化模式,顶板锚索应力平均变化率、峰值应力均显著高于巷帮相应参数,巷道顶板采动效应较巷帮更为明显;锚索应力峰值点滞后最大收敛变形位置约40 m,采动影响时效相比单一煤层开采大幅延长约35 m,采动应力变化率及其峰值分别降低约53.5%,24.5%,己_(15)煤层采动影响范围约105 m;巷道围岩变形速率与距采煤工作面距离呈现反比例函数关系,在此基础上,进一步推导得出深部近距离煤层群距采煤工作面不同距离处围岩变形速度预测公式,并对比现场原位监测数据验证了该公式的合理性。研究成果可为同类深部近距离煤层群的巷道围岩变形速度预测、巷道支护及采矿技术优化等工程问题提供参考。

Investigation on mining mechanics behavior of deep close distance seam group

Deep close distance seam groups mining accounts for a large proportion in China,but the mining mechanical mechanism of this condition is still not clear,which always results in inefficient mining and the frequent occurrence of accidents.The physical and mechanical properties,deformation and failure characteristics of deep coal are essentially different from those of shallow coal seams.Especially under the conditions of deep close distance seam groups mining,the mutual mining influence of the adjacent working face will lead to more complicated mining stress redistribution process.Aiming at the difficult problems of surrounding rock control in deep close distance seam groups,based on the engineering practice of deep close distance seam group of Ji 14 seam and Ji 15 seam of Pingdingshan Coal Mine No.12,the in situ monitoring tests of convergence deformation of roadway and anchor cable stress were carried out at the intake airflow roadway of Ji 15 31030 working face.Furthermore,the floor failure range of the close distance seam group was calculated theoretically,and the formula of deformation velocity of roadway surrounding rock was deduced.And the mining mechanics behavior of deep close distance seam group was revealed preliminarily.The results showed that:① The theoretical calculation of floor failure depth of Ji 14 seam was about 21.24-30.88 m.② Overlying seam mining led to the change of boundary condition of the seam,resulting in the convergence deformation of the roadway presenting a two stage model of stepwise slow growth stage and exponential rapid growth stage.And the exponential rapid growth stage was the main stage of roadway deformation.Furthermore,the convergence deformation of roof floor of roadway,left and right sides,were about 400 mm.③ Monitoring results of the anchor cables stress presented a two stage evolutionary pattern of “nearly linear growth to decrease by step” with the advancing of mining face,while the average change rate and peak stress of roof anchor cables were significantly higher than the corresponding parameters of the wall parts,which indicated that the mining effect of the roadway roof was more obvious than that of the roadway wall.④ Peak anchor cables stress lagged the maximum convergence deformation about 40 m.Besides,compared to the single seam mining,mining impact aging was significantly extended by approximately 35 m,the changing rate and peak value of mining stress were significantly reduced about 53.5% and 24.5%,respectively.The mining influence range of the Ji 15 seam under closed distance mining conditions was about 105 m.⑤ The deformation rate of the surrounding rock of the roadway was inversely proportional to the distance from the mining face.Based on the relationship,the prediction formula of the deformation velocity of the surrounding rock at different distances to the mining face was further derived,and the field in situ monitoring data was used to verify the rationality of the formula.The research results could provide guidance for engineering problems such as the deformation prediction of roadway surrounding rock,roadway support and mining technology optimization in similar deep close distance seam groups.