Roof sub-regional fracturing and support resistance distribution in deep longwall face with ultra-large length

The increase in the cover depth and length of longwall face leads to some drastic changes in mine pressure occurrence and spatial distribution. Such changes result in a great challenge in surrounding rock control. In order to re- alize an effective control of the abnormal mine pressure occurrences,happening frequently and difficult to be predicted in deep longwall face with ultra-large length,the roof rupture characteristics and support resistance distribution in such a longwall face are investigated. Pre-existing fracture development significantly increases due to the increase of cover depth. The fracture size and orientations obey lognormal and normal distributions,respectively. The main roof with ran- domly distributed fractures is reconstructed based on such statistical distributions and DFN method. The large length of longwall face increases the probability of the existence of fractures in exposed main roof. Sub-regional rupture model is established for the main roof with one and two fractures,whose limit load-bearing capacities are achieved. The mechan- ical condition for the occurrence of the sub-regional rupture of main roof and its subsequent migration is achieved using upper bound theory. Spatial distribution of the broken blocks after the main roof fracturing is non-uniform. The block volume in the middle section of the longwall face is small while that of the blocks on two sides of the longwall face is relatively large. Such distribution reasonably explains the non-uniform distribution of the support resistance along the dip direction of the longwall face. The theoretical conclusions are in good accordance with the experimental results and field measurement.