正断层下盘开采应力演化及断层阻隔效应连续-非连续方法模拟

Numerical simulation of evolution of stress and fault barrier effects during normal fault footwall mining based on a continuum-discontinnum method

断层破坏了采场岩层的连续性,应力由断层一盘向另一盘的传播过程将受到断层的阻隔,从而引起断层附近应力集中,极易诱发煤矿灾害.开展采动条件下断层附近应力和煤层支承压力的演化以及断层阻隔效应研究对于煤矿灾害的预防具有重要意义.以自主开发的拉格朗日元与离散元耦合连续-非连续方法为基础,为了处理煤层离散单元形成的聚集体仍能承受超过自身承载能力的问题,采用了应力跌落方法;为了模拟时间较长的煤炭开采过程,采用了准静力计算模式.根据济三煤矿6303工作面的地质条件建立更准确的力学模型,其中,在断层上盘下端面施加垂直向上的适当均布载荷,以克服传统力学模型的应力集中问题.模拟了正断层下盘开采条件下岩层的运动过程.通过在断层上盘断层附近布置多个测点,获得了不同测点的正应力和切应力的演化.详细描述了断层阻隔效应.研究了开采速度对不同测点正应力、切应力和煤层支承压力的影响,定性探讨了开采速度快慢与断层阻隔效应强弱的关系.

The fault destroys continuity of strata in the stope,and processes of stress propagations from the upperwall of the fault to the footwall of the fault or the opposite will be barriered by the fault,leading to stress concentrations in the vicinity of the fault.Thus,coal mine disasters are easily induced.Studies of evolution of stresses in the vicinity of the fault and abutment pressures as well as the fault barrier effect induced by mining are especially important to predict and prevent some disasters.Based on a hybrid continuum-discontinuum method where the Lagrangian element method and discrete element method are combined,the stress drop method was used for assemblies composed of discrete coal seam elements to treat the problem that elements where cracking is impossible can still possess the excessive load-carrying capacity,and a quasi-static mode was used to simulate the long process,such as mining in coal mines.An accurate mechanical model was established based on the geological conditions of the 6303 working face in 3-rd Jining coal mine.In order to overcome stress concentration problems caused by the fault slip restriction due to limited displacements at the base of the traditional mechanical model,an appropriate uniform stress was applied at the base of the upperwall of the fault.Strata motion processes were simulated induced by normal fault footwall mining.Evolution of normal stresses and shear stresses for different monitored nodes were obtained by arranging nodes in the vicinity of the fault in the upperwall of the fault.In a stratum,we found that the deeper the monitored node depth is,the greater the normal stress and the shear stress are when the working face is far away from the fault,and that the closer the monitored node is to the middle of the stratum,the greater the normal stress is and the smaller the shear stress is when the working face is close to the fault.Fault barrier effects were described in details by investigating the widths of regions with lower maximum principal stresses and minimum principal stresses in the hard and thick stratum of the upperwall in the vicinity of the fault during mining.Effects of mining velocities on normal stresses,shear stresses for different nodes and abutment pressures were studied.The relation between mining velocities and fault barrier effects was qualitatively discussed.The faster the mining velocity is,the larger the peak value of abutment pressure is and the more obvious fault barrier effects are.