浅埋煤层长壁工作面围岩动态结构及应力特征分析

Analysis of dynamic stress characteristics and surrounding rock structure in shallow-buried longwall mining face

地下煤层开采后的覆岩结构是覆岩破断和运移的结果,实质是煤层开采后围岩应力重新分布的表现。以浅埋深长壁工作面围岩应力结构为研究对象,利用数值模拟和理论分析方法,从煤层开采后围岩应力场分布规律入手,研究了围岩应力结构的形成与失稳过程,分析了覆岩受力情况。结果表明:浅埋工作面开采后的采场围岩中形成类椭球体的高应力区域,该应力承载结构随着工作面开采在沿工作面倾向、走向及垂直高度上不断发展变化,直至基岩层全部断裂后失稳破坏;初次失稳破坏后,该空间应力承载结构的后方支撑点会迁移至采空区压实矸石上,继续对工作面回采空间提供围岩应力的承载,其形成与失稳是受工作面回采影响的动态演化过程。基于此建立该空间应力结构沿工作面走向的承压拱力学模型,推导出其在覆岩中的形态参数方程和极限状态下的高度及跨距。根据极限承压拱迹线为各岩层弯矩为零的连接线,得到了承压拱迹线上任一位置处的力学状态。结合浅埋深煤层开采后基本顶及其基岩层周期性断裂特征的实践,认为承压拱结构的发展变化规律符合“悬臂梁-铰接岩梁”结构失稳特点,所得结论为浅埋深工作面顶板结构形式及其稳定性研究提供参考。

The overlying structure formed after underground coal seam mining is the result of breaking and migration of overburden strata,which is essentially a manifestation of the redistribution of stress in the surrounding rock after coal mining.Taking the stress structure of surrounding rock in shallow-buried long wall working face as the research object,using numerical simulation and theoretical analysis methods,starting with the distribution of stress field in surrounding rock after coal seam mining,the formation and instability process of surrounding rock stress structure are studied,and the overburden is analyzed from the point of stress field distribution law.The research results show that high stress zone of ellipsoid-like shape can be formed in the surrounding rock stress field after mining in shallow working face.The stress-bearing structure continuously develops and changes with the advance of working face until all the bedrock breaks and loses instability.After initial instability and failure,the rear support points of the spatial stress-bearing structure will migrate onto compacted gangue in the gob and provided support for surrounding rock.The formation and instability of spatial stress bearing structure is a dynamic evolution progress affected by mining face.Based on this,a pressure-bearing arch mechanics model of the spatial stress structure along the direction of the working face is established,and its morphological parameter equation in the overburden and its limit state height and span are derived.The mechanical state at any position on the axis of the pressure-bearing arch is obtained from point of the trace line of ultimate bearing arch is on the connection line where the bending moment of each rock layer is zero.Combined with the practice of the characteristics of the periodical fracture of the basic roof and its bedrock after mining in shallow coal seams,it is believed that the development and change law of the pressure-bearing arch structure is consistent with the“cantilever beam-articulated rock beam”structure instability characteristics.The results provide reference for the study of roof structure and stability of shallow buried working face.