Dynamic Response of Pillar Workings Induced by Sudden Pillar Recovery

When residual pillars are extracted in a short time in room and pillar mining, the load transferred from the removed pillar acts on neighbouring pillar workings in a dynamic manner. This study aims to investigate the instability of large mined-out areas triggered by dynamic disturbance resulting from residual pillar recovery. A mechanical model combining the pressure arch theory (PAT) based method and structural dynamics was first established to assess the stress state and deformation of a pillar subjected to combined effects of static and dynamic loads. The process of residual pillar recovery and potential induced instability of neighbouring pillar workings in a five-pillar system was further numerically simulated in both static and dynamic modes, and the response of adjacent pillars was investigated. It was found that the induced disturbance to a pillar can be characterised by the dynamic amplification coefficient R, the ratio of the increased vertical pillar load to the transferred load. R_max can exceed 1.5 or even approach 2 in practical pillar recovery using the blasting method. Modelling results showed that while pillar workings adjacent to a removed pillar remain stable in static analysis, violent and large-scale pillar collapses can be triggered in the event of quick pillar recovery of blasting method. Results indicated that when the dynamic effect of pillar recovery is not considered, the load undertaken by adjacent pillar workings would be largely underestimated. To ensure mining safety, the induced dynamic effect should be accounted for in the design of the pillar recovery method.