Safety mining evaluation of middle abandoned coal seam in “upper pillar-lower longwall” composite mining areas

Based on the safety mining of residual coal in the middle with “upper pillar-lower longwall” composite re- sidual areas in Baijiazhuang coal mine,the strata collapsing characteristic and the distribution of vertical stress around residual coal seam under the multiple influence of mining are studied with similarity and numerical simulation. At the same time,based on the previous studies,combined with the theory of elastic-plastic mechanics,the calculations model is established for the damage zone of rock strata between coal seams caused by mining upper-lower coal seams in com- posite residual areas,the above researches are integrated and provide the feasibility determination of middle residual coal seam. Research results show that:① Similar simulation experiment shows that the influence of mining upper-lower coal seams does not damage the macro-continuity of middle residual coal seam,and in the process of mining middle re- sidual coal seam,the overlying strata structure is relatively stable;② Numerical simulation experiment shows that the distribution range of abutment pressure and plastic zone are matched on the whole,which can evaluate the damage zone of rock strata between coal seams after mining upper-lower coal seams,the damage scope is across the upper in- terburden,while partial lower interburden is damaged;③ Through the theoretical analysis,the face of middle residual coal seam is mainly affected by mining upper coal seam,in the upper coal seam mining damage range,the stability of overlying strata is poorer in mining residual coal seam No. 7,the stability of overlying strata should be paid more atten- tion and the reasonable support measures should be taken timely to ensure a safe mining.