Influence of upper-bottom pillar mining on temporal and spatial evolution of stress in rock strata around middle residual coal seam

In order to ensure the safe mining of middle residual coal seam with top-bottom pillar gobs,the influence of upper-bottom pillar mining on the temporal and spatial evolution of vertical stress around middle residual coal seam was studied with the similarity and numerical simulation based on the occurrence conditions of NO. 7 middle residual coal seam in Baijiazhuang coal mine,China. Research results show that:① The strata above coal pillars and pillar- mining zones are evolved to stress concentration and reduction zone respectively after bottom-pillar mining,while the degree will be enhanced after upper-pillar mining. ② The vertical stress evolution of “initial balance-initial wave bal- ance-new wave balance” not only reflects the temporal and spatial superposition effect of abutment pressure caused by the multiple pillar mining of upper-bottom coal seams,but also is closely related with combined pressure relief effect. ③ The vertical stress distribution of residual coal seam also presents wave characteristics after multiple-pillar mining.