Abstract: To solve the problems of the sharply appeared mine pressure and determination of the support working resistance in mechanized caving mining process of the ultra-thick coal seam, a structural model of cantilever beam-masonry beam is considered. When the support resistance is low at the time of face pressing, the subsidence of masonry beam results in the rotational deformation and the failure of cantilever beam. Furthermore, it leads to the slide breaking and pressing frame of the cantilever beam and the violent behavior of mine pressure. A mechanical model of breaking cantilever beam structure with a central crack is thus established. The effect of a serious of factors on the failure of the cantilever beam is analyzed by using fracture mechanics theory, and the expression of the support load is derived. The results show that the angle and length of the crack are the main factors influencing the failure of the cantilever beam. In addition, the support load is also relevant to other factors such as the falling step distance of the masonry beam. Based on the geological conditions of the fully mechanized working face 8102 in Tashan mine, the calculated support loads are used to verify the theoretical analysis. The results are of practical significance for analyzing the support load of ultra-thick coal seam mining and for providing reasonable selection of support to reduce the roof accident.

Key words: ultra-thick coal seam, fully mechanized caving mining, structure of cantilever beam-masonry beam, oblique crack, support working resistance