含隐伏断层煤层回采诱发底板突水影响因素研究

Study on factors influencing groundwater inrush induced by backstopping of a coal seam with a hidden fault

针对具体地质条件,采用FLAC^(3D)的固液耦合模式,利用变参数流变模型对含隐伏断层缺陷煤层诱发底板滞后突水影响因素及滞后突水机理进行研究。结果表明:滞后突水是由底板岩体的变形和破坏所引起,其影响因素不仅与隐伏断层与煤层的空间关系及承压水水压有关,而且与隐伏断层发育程度及其与煤层间的空间距离有关;隐伏断层顶界面处的应力随工作面的持续推进先增加后松弛再增加,应力变化导致对应位置处的岩体先压缩后膨胀再压缩,隐伏断层顶界面处的最大垂向位移与煤层埋深之间存在线性关系,而与水压及隐伏断层顶面与煤层间距之间均存在幂指数关系;煤层回采致使地应力重新分布,重新分布的应力影响到底板岩体的渗透能力,使裂隙内的水将静水势能转变成动能,进而对裂隙壁面产生冲刷和扩张作用,这种影响具有时效性,其为滞后突水机理研究的核心内容和关键问题。通过计算再现了不同因素影响下煤层回采过程中底板采动裂隙形成、隐伏断层损伤破坏到突水通道形成的全过程,揭示了含隐伏断层构造底板突水通道的形成机制。研究结果对承压水上含隐伏断层缺陷煤层安全回采具有重要的参考价值。

Based on detailed geological conditions of a specified mine, a FLAC^3D solid-liquid coupling model and a variable parameter rheological model are employed to investigate the influencing factors and mechanism of delayed groundwater inrush induced by a coal seam with a hidden fault. The results show that the delayed water inrush is caused by floor rock mass deformations and damages; the influencing factors are related not only to the spatial relationship between the hidden fault and coal seam and the pressure of confined water but also to the development level of the hidden fault and the spatial distance between the hidden fault and the coal seam. The stress at the upper boundary of the hidden fault follows a pattern of increase-relax-increase with the progression of the working face. This stress variation leads to compression-expansion-compression of the rock mass at the corresponding position. The maximum vertical displacement at the hidden fault＇s top boundary is linearly related to the coal seam＇s burial depth and has an exponential relationship with water pressure and space between the top of the hidden fault and the coal seam. Coal seam mining redistributes the ground stress and the redistributed stress affects the permeability of the floor rock mass. Water in the fracture transforms the potential energy into kinetic energy, which subsequently washes and expands the fractured wall. This effect is time variant and is the key to understanding the delayed water inrush mechanism. By calculations, this paper has reproduced the complete process of floor mining fracture formation and hidden fault damage and water inrush channel formation during coal seam mining under various influencing factors. It reveals the mechanism of water inrush channel formation at the floor of the hidden fault structure. This research result has important significances for safely mining a coal seam with a hidden fault over a confined water layer.