Progressive failure processes and mechanisms of disasters caused by interrelated failure of residual coal pillars and rock strata.

The increasing number of closed/abandoned mines being reused has become a concern for people. However, a large number of coal pillars were left behind in the closed/abandoned mines. Before effectively utilizing the underground space of mines (CO goaf storage, etc.), it is necessary to study the stability of the residual pillars and rock strata. However, limited laboratory experiments and numerical simulation tests have been carried out to understand the relationship between residual pillars and strata in the context of their failure process and mechanism. In this study, the progressive failure and movement of the pillars and strata during the multi-seam mining is simulated using a physical model and numerical simulation. In addition, the failure mechanism was analyzed. The results suggest that the failure process of the pillar is strongly related to the rock strata. The mining of the below seam will bring about not only the collapse of the above strata, but also penetrate the gob of the overlying seam, and then cause the roof of the overlying seam to further collapse. The damage zone acting on the pillar increases accordingly, and the pillars are also gradually damaged. When the pillar is completely destroyed, it will further cause the stable strata to fracture, collapse and become unstable, and a rock burst may be formed. It is also found that under the effect of the stress concentration of the pillar, the floor rock will be damaged to a certain depth. When the collapse height of the overlying strata overlaps with the failure depth of the floor due to the stress concentration, it is more likely to bring about the occurrence of rock burst. The mechanisms of progressive failure of the residual pillars and rock strata revealed by this study offers guidance for the control of disasters, and also provides a reference for the stability research during goaf utilization in the later stage.