中深埋厚煤层开采地下水位动态变化规律及形成机制

Dynamic law and mechanism of groundwater induced by medium-deep coal mining

  • 摘要: 煤炭开采对风化基岩含水层和潜水含水层的影响是榆神矿区“保水采煤”研究的重点。为揭示榆神矿区风沙滩地区中深埋厚煤层开采条件下地下水动态变化规律和机理,以榆神矿区中部某矿首采工作面(01工作面)为研究区,采用钻探、地下水位观测、野外实地探查和综合分析等方法,研究了采动地下水动态变化规律及其与覆岩损害和地表下沉之间的耦合关系。结果表明:① 风化基岩含水层水位随回采表现出“先下降后回升”并恢复至初始水位的动态变化过程,中间可分为“快速下降”、“回升恢复”和“稳定波动”3个阶段,平均持续时长为102 d。在水位快速下降阶段,水位最大降深、平均下降速率均呈正态分布,且与距工作面中心距离呈指数函数关系;水位回升恢复阶段,持续时长和平均回升速率与距工作面中心距离呈负相关关系;② 当潜水含水层分布局限、侧向补给缺乏时,潜水含水层水位出现“先下降后回升”和“持续下降”至稳定2种动态变化规律,且均未恢复至初始水位;③ 面内风化基岩含水层水位动态变化过程与风化基岩层的剧烈下沉密切相关,风化基岩层下沉速度的增大和减小过程分别对应水位的下降和回升过程,水位下降则与其下沉、临时性裂隙和离层发育有关,水位回升则是下沉减缓、临时性裂隙和离层的闭合以及含水层侧向补给因素有关;面外风化基岩含水层水位的动态变化则与其侧向补给有关;④ 面内潜水位的动态变化过程与地表下沉密切相关,其水位下降与地表活跃阶段早期剧烈下沉具有同时性和一致性,地表下沉造成的潜水水头差和潜水的渗流出露是造成水位下降的主要原因;水位回升则是地表进入活跃阶段后期和衰退阶段,高位潜水侧向补给和大气降水补给造成的;面外潜水位持续下降则是潜水侧向渗流和补给不足造成的;⑤ 中深埋煤层开采条件下,导水裂隙带一般不会导通至风化基岩层,风化基岩含水层水和潜水含水层水不会因采动导水裂隙而漏失,风化基岩水位可恢复,潜水含水层水位会因采动地表移动发生变化。

     

    Abstract: The influence on underground water aquifers especially weathered bedrock aquifer and phreatic aquifer caused by middle-deep coal mining has become the focus of protection of water resources.In order to systematically reveal the dynamic law and mechanism of groundwater induced by the mining of middle-deep buried and thick coal seam in Yushen mining area,the first coalface of a coal mine was taken as the study area,the methods of drilling,groundwater level observation,field exploration and comprehensive analysis were adopted to study the dynamic law and coupling relationship with overlying rock damage and surface movement.The results show that with the advance of coal mining,the water level of the weathered bedrock aquifer located in the curved subsidence zone shows a dynamic process that is falling first and then rising to the initial water level.The dynamic process is divided into four stages,namely “start-up stage”,“rapid decline stage”,“recovery stage” and “stable stage” with an average duration of 102 days.In the stage of rapid decline of water lever,the maximum depth and average falling rate of water level are in accordance with the exponential function with the distance from the center of the working face,while in the stage of water level rising-recovery,the duration and average rising rate are negatively correlated with the distance from the center of the working face.When the distribution of the phreatic aquifer is limited and the lateral recharge is lacking,the water level of the phreatic aquifer located in the curved subsidence zone has two dynamic changes:“falling first and then rising” and “continuous descending” to stable,and both of them have not recovered to the initial water level.The dynamic process of water level of the weathered bedrock which located in the working face is closely related to the bending and subsidence of the bedrock.The increasing and decreasing process of subsidence velocity of weathered bedrock corresponds to the falling and rising process of water level,respectively.The decline of water level is related to its subsidence,temporary fissures and the development of detachment,while the rise of water level is related to the slowing down of subsidence,the closure of temporary fissures and separations and the lateral recharge of aquifers.The dynamic process of water level of the weathered bedrock outside working face,is controlled lateral replenishment.The dynamic process of phreatic water level in working face is closely related to the surface subsidence,and the falling period of the water level is consistent with the violent subsidence in the early stage of surface active period.The diving head difference caused by surface subsidence and the seepage exposure of phreatic water are the main reasons for the drop of water level,while the rise of the water level is caused by the slow subsidence of surface,lateral recharge of high level of phreatic water and the replenishment of atmospheric precipitation.The main reason of the continuous decline of phreatic water level outside the working face is the lateral seepage and insufficient recharge.Under the mining condition of medium and deep buried coal seams,the water diversion fracture zone generally does not lead to the weathered bedrock,the water of the weathered bedrock aquifer and the phreatic aquifer will not be lost due to the mining water diversion fracture,and the water level of the weathered bedrock can be restored.The water level of phreatic aquifer will change due to mining surface movement.

     

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