Feasibility analysis of residual coal mining in the middle of unequal width composite pillar mining area

The mining of middle residual coal seam in the unequal width composite pillar mining area was selected as the as research object. With the coupled methods of numerical simulation, similar simulation and mechanical analysis, the feasibility of residual coal mining in the middle of unequal width composite pillar mining area was systematically analyzed from three aspects including the stability of residual coal pillar, surrounding rock stress distribution, and rock structure stability. The results showed that: the stability of wide coal pillars in the residual mining area was stronger than that of narrow coal pillars under the composite mining influences. During the mining process of the middle coal seam, the abutment pressure superimposed with the concentrated stress in the residual coal pillar, which led to the pre-failure of narrow coal pillars and strengthening of stress concentration of wide coal pillars. After the composite pillar mining, the "residual coal pillars and upper control layer" inverted continuous beam rock mass structure and the "residual coal pillars and bottom bearing layer" continuous beam rock mass structure were formed. During the mining process of middle coal seam, the control layer in the upper interburden strata gradually broken and failed. Especially when the workface passed the wide coal pillar, the interbueden strata cut off, which would induce the system failure of the "residual coal pillars and upper control layer" inverted continuous beam structure and the strong strata pressure behavior. Moreover, the stability of "residual coal pillars and bottom bearing layer" continuous beam rock mass structure could be maintained overall. The residual coal mining in the middle of unequal width composite pillar mining area could achieve good feasibility. When the working face passed through the high stress area corresponding to overlapping residual coal pillar in the composite pillar mining area, it is necessary to adopt the prevention and control technical measures such as backfilling along the coal pillars, pre-splitting of residual coal pillar and roof strata to reduce the strong mining pressure. This study can provide good theoretical support for safe and high-efficient mining of residual coal mining in the middle of unequal width composite pillar mining area. © 2021, Editorial Board of Journal of Mining & Safety Engineering. All right reserved.