Research on roof breaking laws of steep and ultra thick coal seam

In order to study on the roof breaking law of fully-mechanized top coal caving face in steep and ultra thick coal seam. Taking the45° coal seam in the nor thern mining area of Wudong Coal Mine as the research object. In this paper, the stress model of the roof under fully-mechanized top coal caving face in the steep and ultra thick seam was established, the moment equation of the roof was obtained, the basic top breaking position was analyzed, and then the basic roof was established based on the theory of cantilever beam. Stress equation was used to analyze the basic breaking length in different mining environments. At the same time, 3DEC softw are was used to calculate the breaking length of roof under different mining conditions. The results showed that the fully-mechanized top coal caving in the steep and ul tra thick seam had the first break in the middle. With the increases of the basic roof thickness, the breaking length of the basic roof decreased linearly. With the increas e of the height of the mining section, The breaking ratio was increased by parabola. The useing of drilling on the scene peep, accessed to the basic top of the damage, monitoring results and theoretical analysis were same, for the roof monitoring and protection of coal was important.