Abstract: This study aims to study the damage and rupture laws of the main roofs between coal seams with a close distance. A continuum damage model was adopted to investigate the damage laws of floor caused by mining the upper coal seam. Morever, the main roofs were clearly classified based on their positions in damage area of the floor in the goaf. Thus, an initial fracture span formula was obtained for the damaged main roofs. The numerical calculation results show that the damaged area in the floor is spoon-shaped and the damage value decreases from the damage core area to the marginal area. The main roofs between coal seams can be divided into three types, including no damage, partial damage and complete damage. In addition, the influence of three types of main roofs on the behaviours of the lower strata decreases successively. The fracture length declines with the increase of the damage value, until the limit damage value occurs, which results in the fracture length approaching to zero. The height-length ratio of critical blocks formed from the damaged main roofs increases and the voussoir beam slides easily to a great extent. The laws of damaged main roofs are verified in Xiegou coal mine.

Key words: close distance coal seams, damaged main roof, damage value, classification, fracture length