上下盘开采断层滑移失稳诱发地表异常沉陷机理研究

Mechanism of abnormal subsidence induced by fault slipping instability during mining on hanging-wall and foot-wall

当工作面上覆岩层中含有断层,开采造成断层带岩体滑移失稳时,断层露头处地表移动变形值往往异常增大。含有断层时的地表移动变形规律与不含断层时具有显著差别。为研究上下盘开采断层滑移失稳诱发地表异常沉陷机理,通过理论推导建立上下盘开采断层滑移失稳力学模型和土体近似悬臂断裂模型,并结合数值模拟和相似模拟实验对比分析上下盘开采断层滑移失稳机理及其难易程度。研究结果表明:断层露头处地表异常沉陷是断层滑移失稳后土体在断层露头处受悬臂作用而发生断裂的结果,上盘开采断层露头附近地表裂隙或台阶偏向采空区外侧,下盘开采断层露头附近地表裂隙或台阶偏向采空区;上盘开采断层可稳定区域比下盘开采大,上盘开采断层更容易维持稳定,下盘开采断层露头处地表更容易产生台阶下沉;上盘开采随断层倾角增大,断层稳定性变差,下盘开采当断层倾角小于断层带岩体内摩擦角时,断层一定会滑移失稳,而下盘开采随断层倾角增大,断层稳定性增强;下盘开采断层露头处剪应力与正应力的比值为上盘开采的5倍左右,下盘开采断层带岩体更容易滑移失稳;断层作为岩体中天然弱面存在,对采动应力的传递具有阻断效应。研究结果对分析断层影响下的地表沉陷规律及断层露头处建、构筑物的保护具有一定意义。

With faults in overlying strata,the slip and instability of rock mass in the fault zone induced by mining tend to cause abnormal increase in the surface movement deformation at the fault outcrop.The displacement and deformation of the surface with faults is markedly different from that without faults.To obtain the mechanism of abnormal subsidence induced by fault slipping instability during mining on hanging-wall and foot-wall,the mechanical model of fault slipping instability during mining on hanging-wall and foot-wall and the fracture model of soil mass similar to cantilever have been built through theoretical derivation.At the same time,a comparative analysis of the mechanism of fault slipping instability during mining on hanging-wall and foot-wall and its complexity has been conducted through numerical simulation and similar simulation.The study has shown that firstly,the abnormal subsidence at fault outcrop is caused by fault slipping and rock mass cantilever broking,and the surface fissure or step subsidence near fault outcrop would move outward gob when mining on hanging-wall,while it’s converse for mining on footwall.Secondly,the stable area of hanging-wall mining fault is wider than that of the foot-wall mining fault.Therefore,it is easier for hanging-wall mining fault to maintain stability,and the step subsidence is more likely to happen at the surface of foot-wall mining fault outcrop.Thirdly,in hanging-wall mining,the stability of the fault worsens as the fault dip angle increases,while in foot-wall mining,the fault is destined to slip and lose stability when its dip angle is less than friction angle of the rock mass,and the fault stability intensifies as its dip angle increases.Fourthly,when the ratio of shear stress and normal stress at fault outcrop during foot-wall mining is around five times that of hanging-wall mining,it’s more prone for the rock mass in the fault to lose stability during foot-wall mining.Fifthly,fault,as a naturally weak surface of rock mass,has blocking effect on the transfer of mining stress.The research has great significance for the research on subsidence laws under the influence of faults and the protection of the buildings and structures at the fault outcrop.