基于微震监测的董家河煤矿底板突水通道孕育机制

Preparation mechanism of water inrush channels in bottom floor of Dongjiahe Coal Mine based on microseismic monitoring

针对董家河煤矿工作面断层突水问题,通过构建工作面微震监测系统,对断层区域底板岩体微破裂信息进行分析,再现了过断层前后底板岩体微破裂萌生演化过程。同时将微破裂信息和岩石破裂过程分析系统RFPA2D结合,研究底板断层围岩导水裂隙带发育过程中应力场的变化规律。结果表明:①根据微震事件分布结果分析,工作面位于断层前方85 m时,底板断层开始发生微破裂。过断层前断层附近底板微破坏深度达到25 m,底板具有分段局部破坏特征;过断层后,最大微破坏深度为35 m,微破裂逐渐贯通。②基于微震能量密度分布结果分析,过断层前高能量密度集中区走向长度约15m,位于煤层下方5~25m,而紧邻煤层的5m范围内的断层仍处于稳定状态。过断层后高能量密度区向上盘采空区及深部扩展,沿工作面走向扩展至上盘采空区约80 m范围内,深度方向扩展至煤层下方约35 m。③基于微震监测和数值模拟结果分析底板岩体破坏过程,将底板突水通道扩展过程分为过断层前和过断层后两个阶段,过断层前煤层下方25 m附近断层围岩首先发生微破裂,并沿断层向上扩展,煤层下方5~25 m发生局部微破裂但并未形成贯通;过断层后微破裂自上而下扩展并逐渐贯通,形成突水通道。④基于数值模拟断层应力演化规律分析,过断层前,断层剪应力为负值且逐渐减小,断层上盘有向下滑移趋势,深度越大剪应力越快达到最大,围岩自下而上发生压剪破坏。工作面位于断层附近时,剪应力方向迅速反转并达到最大,断层上盘在承压水作用下有上升趋势,围岩自上而下发生拉破坏且逐渐贯通形成导水通道。

To overcome the water inrush problem of working face at Dongjiahe coal mine,a microseismic monitoring system was installed to analyze the microcrack data from baseplate of fault zone.The initiation and evolution process of microcracks in baseplate was reconstructed during the working face passes through the fault.Also,the microcrack data was combined with Realistic Failure Process Analysis(RFPA2D)system to study the variation law of stress fields during the evolution process of water-conductive fissure zone in wall rocks of baseplate fault.The results showed that:①according to the analysis of microseismic event distribution,microcracks occurred when working face is 85 m ahead of the fault.The depth of microcracks in baseplate reached 25 m before working pace passing through the fault and the baseplate has a sectioned local failure characteristics.After working face passing through the fault,the maximum depth of microcracks reached 35 m and microcracks are gradually transfixed.②According to the analysis of microseismic energy density distribution,the concentration zone of high energy density before passing through the fault was about 15 m in strike length,and located in 5-25 m beneath the coal layer.Meanwhile,the fault located within 5 m range of coal layer remained stable.After passing through the fault,the high energy zone expanded to upper goaf and deeper zone,to around 80 m range into the upper goaf along the working face,and around 35 m range beneath the coal layer.③According to the microseismic monitoring and numerical simulation results,the expansion process of baseplate water inrush tunnel could be divided into two phases as before passing the fault and after passing the fault.Before passing the fault microcracks occurred initially in the wall rocks of fault around 25 m beneath the coal layer,and expanded through the fault.There were microcracks occurred in 5-25 m beneath coal layer but not yet transfixed.After passing the fault,the microcracks expanded from top to bottom and formed a water inrush tunnel.④According to the analysis on the evolution law of fault stress based on numerical simulation,before passing the fault,the shear stress of the fault was a negative value and gradually decreasing.The upper part of the fault tended to slip downwards.The greater the depth the faster the shear stress reached its extremum,resulting in a compression and shear failure in wall rocks from bottom to top.Upon the working face reached near the fault,the shear stress reversed rapidly and reached its maximum.The upper part of the fault tended to go upwards under the action of confined water.The surrounding rocks had a pull failure from top to bottom,and cracks gradually transfixed,forming a water conductive tunnel.