Top coal arching mechanism and arch removal strategies in fully mechanized top coal caving mining of ultra-thick coal seam

Based on in-situ measurement and theoretic analysis,the top coal arch phenomenon and arch forming mech- anism are elaborated in the fully mechanized top coal caving mining of ultra-thick coal seam in Tashan Coalmine,Da- tong,China. A top coal analytic model formed by arching blocks in face contact is proposed,which takes the axis of the arch in the form of parabola. The study derives the parameters of height-span ratio of top coal arch that affects the effi- ciency of top coal recovery,where the supporting plane angle and coefficient of friction involved in the height-span rati- o are analyzed. The countermeasure strategies against the top coal arching effect are put forward and performed in prac- tice. As a result,the recovery ratio of top coal increased by 6. 92% that shows the significance for the efficient recovery of coal resources.