覆岩结构类型与开采覆岩损害特征分析

煤层开采打破了上覆岩层原有的平衡,必然引起岩层的移动、破断,导致应力场和裂隙场的改变,工作面出现矿压显现。上覆岩层的岩性和组合结构对工作面开采覆岩损害特征分布影响显著,一般岩性越坚硬,上覆岩层应力集中程度越高,采动裂隙越发育,矿压显现也越明显;坚硬岩层尤其是关键层对覆岩的破断运动起控制作用,覆岩破断发展到一定层位后软弱岩层往往是抑制覆岩破断进一步向上发展的关键。当工作面上覆岩层同时存在远近场关键层时,近场关键层的周期性破断引起裂隙带范围内岩层的运动和工作面周期来压;而远场关键层的周期性破断导致地表裂缝或台阶下沉,工作面压力急剧上升,有时甚至导致煤矿动压灾害,尤其是远近场关键层同步破断时动力现象更明显。通过地面钻孔使远场关键层提前破断是防止此类动力灾害的关键。

Analysis of Overburden Structure Type and Damage Characteristics of Overlying Strata

Coal mining breaks the original balance of the overlying strata,which will inevitably cause the movement and breakage of the overlying strata,resulting in the change of the stress field and the fracture field and the strata behaviors on the working face.The lithology and combined structure of the overlying strata have a significant influence on the distribution characteristics of overburden damage in the working face.Generally,the harder the lithology is the higher the stress concentration of overlying strata is the more developed the mining fissures are and the more obvious the mine pressure is the hard strata especially the key strata,play a controlling role in the breaking movement of the overlying strata.When the fracture of the overlying strata develop to a certain horizon,the soft strata are often the key to restrain overburden breakage from further upward development.When the overlying strata of the working face have both far and near field key strata,the periodic breakage of the near field key strata cause the movement of the strata within the fracture zone and periodic weighting;while the periodic breakage of the far field key strata result in ground cracks and bench convergence of the working surface,and the face pressure rises sharply,sometimes even leads to dynamic pressure disasters in coal mines.In particular the dynamic phenomena are more obvious when the key strata in the far and near field break synchronously.The key to prevent such dynamic disasters is to break key strata in the far field ahead of time by drilling holes on the ground.