基于裂纹扩展的含隐伏断层底板突水评价

Evaluation of Water Inrush from Floor Containing Insidious Fault Based on Crack Growth

为研究承压水上开采时含隐伏断层底板的安全性,根据断裂力学理论建立导水断层活化扩展的理论模型。将煤层底板看做半平面无限体,把底板中含水层顶部以上的隐伏断层建模为有限宽度板条的倾斜边缘裂纹。根据采场底板的支承压力分布规律,将其简化为若干分段线性载荷加载至底板,纳入断层产状、断层在底板中埋深、工作面推进距离、含水层水压、断层面摩擦角等各种参数,推导得到底板内任意一点的应力公式。将其应用到隐伏断层面上各点,综合考虑各点法向应力、剪应力对裂纹活化的影响,计算得到采动条件下断层面上的有效切应力分布。该有效切应力剔除了裂纹面上摩擦效应对压剪裂纹扩展的影响,将其代入断裂力学相关公式,计算得到隐伏断层前缘的应力强度因子,最后通过定义突水安全指数建立了底板突水判据。以某矿带压开采工作面为例,根据相应水文和地质资料,计算得到在工作面推过隐伏断层的整个过程中断层活化突水危险性的变化规律,所得结论与工作面现场微震监测数据相符,即当工作面推进至采空区位于隐伏断层正上方区域时,断层面承受有效剪切最充分,剪切应力强度因子最大,突水安全指数达到峰值,这与现场微震监测结果中显示的在该推进阶段中,原有隐伏断层附近派生裂隙集中出现、突水危险性最高的结果相符合。

For analyzing the security of floor containing insidious fault while mining above water, a fracture mechanical model is established in order to describe the activation and growth of insidious fault. First, from the beginning of aquifer top in floor, the above part of insidious fault is modeled as an oblique edge crack of finite width plate. Second, involving the effects of normal stress and shear stress for fault activation, effective shear stress distribution in the fault plane is calculated in the mining conditions. Third, according to attitude and burial depth in the floor of fault, distance of face advancing, water pressure of the aquifer, and angle of friction in the fault plane, the compress-shearing stress intensity factor of insidious fault is presented. Finally, the safety index is defined for establishing the criterion of water inrush. Taking a certain coal face mining under pressure for example, in accordance with its hydrologic and geological data, variation of risk about water inrush from activating fault is obtained during the whole face advancing across the fault. The conclusion coincides with microseismic monitoring data at the site. This analysis may provide suggestions for safe and rational coal mining and improve numerical or theoretical models of water inrush in floor.