Research on the weakening technology and the drawing law of top-coal in western shallow-reserved hard and thick coal seam

Based on the data of theoretical analysis and numerical calculation, the paper studies on the caving ability and drawing degree of top-coal in shallow-reserved hard and thick coal seam adopted longwall with top-coal caving mining. Different top-coal weakening technologies are suggested and proved to be effective in field tests and a new concept of loosing top-coal falling and caving is also put forward in this paper. Study indicates the loss of top-coal in gob has periodicity as the periodically moving of the first caving rock in the loosing coal-rock mixture above the drawing opening of hydraulic support.