采动覆岩微震分区演化特征的数值模拟研究

Numerical simulation study on sub-regional evolution of microseismic characteristics of mining overburden rock

为了探究采动覆岩的破裂分区特征与微震演化规律,以某矿井工程地质条件为背景,根据矩张量与颗粒流理论构建了微震模拟方法,实现了对回采工作面覆岩微震演化特征的模拟研究。研究表明:采动覆岩的微震事件矩震级集中在–2.7~–1,微震破裂强度符合常见的正态分布性质,微震发生频次与微震矩震级的关系也满足经典的矩震级–频度关系式;微震事件在采场横向上表现出明显的区域分布特征,采空区左右煤壁中的微震事件先于采空区顶板发生,微震事件围绕采掘空间向两侧发展,且存在一定的超前性与滞后性;当工作面开采一定距离后,采空区上覆岩层的垂向应力表现出“双峰值”特征,微震事件迅速向上延伸,并在上覆软弱岩层内集聚、发育,使得微震事件在竖向上同样表现出明显的分层分布特征;根据采场的应力、位移以及微震分布特征,可以将上覆岩层划分为“横四区”与“竖三带”,各个破裂区域的微震事件破裂类型占比各不相同,煤壁支撑区与离层区分别为剪切型与拉伸型微震事件的主要占比区域。此外,对研究区域建立了微震监测系统,现场监测与数值模拟结果基本吻合,表明构建的微震模拟方法适用性较好,可以从细观层面再现采动覆岩的微震演化过程,研究结果为揭示采动裂隙演化机理提供一定的理论基础。

In order to explore the fracture zone characteristics and microseismic evolution within overburden rock above mining coal seam,based on the geological engineering conditions of a mine,a microseismic simulation method was constructed according to the moment tensor and particle flow theory,and the microseismic evolution characteristics of overburden rock above panels were simulated.The results show that the magnitude of microseismic events in mining-disturbed overburden is between-2.7 and-1,and the microseismic fracture strength conforms to the Gaussian distribution.The relationship between microseismic frequency and moment magnitude also satisfies the classical moment magnitude-frequency relationship.The microseismic events show prominent regional distribution characteristics in the horizontal direction of the panel.The microseismic events in the left and right coal walls of the goaf occur earlier than the roof above goaf,and the microseismic events develop to both sides around the mining space,and there is a certain advance and lag.When the panel is mined for a certain distance,the vertical stress of the overburden above the goaf shows a'double peak'characteristic,and the microseismic events extend upward rapidly and gather and develop in the weak overburden so that the microseismic events also show prominent layered distribution characteristics in the vertical direction.According to the stress,displacement,and microseismic distribution characteristics within overburden,the overburden can be divided into‘four horizontal zones’and‘three vertical zones’.The proportion of microseismic events and fracture types in each fracture area is different.The coal wall supported and bed separation areas are the large proportion areas of shear and tensile microseismic events,respectively.In addition,a microseismic monitoring system was established for the study area.The field monitoring and numerical simulation results are consistent,indicating that the constructed microseismic simulation method has a good applicability and can reproduce the microseismic evolution process of mining-disturbed overburden from the mesoscopic level.The research results provide a theoretical basis for revealing the evolution mechanism of mining-induced fractures.