Dynamic Effect and Control of Key Strata Break of Immediate Roof in Fully Mechanized Mining with Large Mining Height

This paper puts forward the concept of key strata in immediate roof (KSIF) and studied the dynamic effect and control mechanism of KSIF. The results show that KSIR controls the caving of its upper immediate roof strata; the break of KSIR has direct dynamic impact on its lower strata and this impact increases along with the increase of the thickness and hardness of the KSIR and the decrease of the distance to the working seam. The KSIR and main roof can easily form the bilayer structure "Cantilever-Masonry beam." Support work load is affected by the position, thickness, and hardness of KSIR. The support work load increased on the condition of increase of the thickness and hardness of KSIR and the decrease of the distance to the face.