高位硬厚岩层下采动裂隙和支承应力演化特征及其对瓦斯运移的影响

Evolution characteristics of mining-induced fracture and abutment stress under high-position hard thick stratum and its effect on gas migration

针对上覆高位硬厚岩层的结构特征和受力状态,建立了均布载荷和体积力共同作用的力学模型,得到了硬厚岩层破断形式的力学判据。采用相似材料模拟试验及离散元数值模拟,研究了高位主关键层下覆岩采动裂隙和支承应力的演化规律及其对瓦斯运移的影响,并采用工程实例验证了研究结果。研究表明:高位主关键层条件下,覆岩采动裂隙发育、煤岩体支承应力分布、卸压效果都发生了明显变异,主关键层阻隔了向上发育或传递。主关键层下方形成中部梯形压实区和两侧平行四边形破裂区,破断裂隙呈类"马鞍"形分布,其底部离层量分布按照"单谷"、"倒梯形"、"双谷"形态演化;煤岩体支承应力集中程度较高,影响范围较大,主关键层破断运移后明显下降。主关键层下方存在采空区卸压裂隙发育区,游离瓦斯可通过破断裂隙运移至主关键层底部的负压离层空间,主关键层运移时可能诱发地面钻孔瓦斯动力现象。

In view of the structural characteristics and stress state of overlying high-position hard thick stratum,a mechanical model affected by the interaction of uniform load and body force was built.The mechanical criterion of hard thick stratum breaking mode was obtained.Through similar material simulation test and discrete element numerical simulation,the evolution characteristic of overlying mining-induced fracture and abutment stress and its effect on gas migration under the high-position main key stratum was studied,and the research results were validated with an engineering case.The re sults have shown that significant variations occur to the mining-induced fracture development,abutment stress distribution of coal and rock,and stress relief effect under the high-position main key stratum conditions;the upward development or transfer is blocked.A trapezoidal compaction zone forms in the middle,parallel quadrilateral rupture zones form in both sides under the main key stratum,and the fractures develop in a shape of a saddle.Separation distribution at the bottom of main key stratum evolves from the shape of ＂single valley＂ to the shape of ＂inverted trapezoid＂ and then to the shape of ＂two valleys＂.High abutment stress of the coal and rock under the main key stratum has high concentration and a large scope of influence,but it decreases significantly after the fracture and migration of the main key stratum.Gob region of stress relief and fracture development exists under the main key stratum,and free gas could migrate to the separate strata space with negative pressure through the breaking fractures,which would induce the ground borehole gas dynamic phenomenon when the main key stratum moves.