Overlying strata movement and weighting mechanism of extra shearing height working face

For the large one-time extraction space, prominent scale effect of ground control, intense mine pressure manifestation and unclear mechanism of pressure relief in ultra-high mining height working faces, the roof fracture structure, movement law, pressure relief mechanism and control methods of the world's first 10 m ultra-high mining height fully mechanized working face were investigated by numerical simulation, theoretical analysis and microseismic monitoring. The results reveals a combined roof fracture form of "low-position 0-40 m cantilever beam (equivalent immediate roof) + high-position 40-100 m masonry beam (key layer structure group)". Affected by the instability of the medium and high-position "key layer structure group", there is a regular "large and small cycle pressure relief" phenomenon in the working face. A single large cycle contains multiple consecutive strong pressure reliefs with high pressure relief intensity. The vertical continuous fracture of roof strata from "bottom to top" and "top to bottom", and the triggering of the vertical "up and down linkage cycle instability" of the medium and high-position key layer are the key inducements for the significant increase in the step distance, continuous distance and pressure relief intensity of the large cycle. At the same time, the stress evolution of the surrounding rock in the stope is controlled by the fracture process of the medium and high-position key layer, and the intervention and control of the fracture movement of the latter is the key to regulating the mine pressure in the stope. ③The fracturing and weakening of the low-position thick and hard rock strata can enhance the stability of the high-position "key layer structure group" and block the vertical "up and down linkage cycle instability" process of the rock strata, thereby weakening the risk of strong pressure relief in the large cycle. Based on the prevention and control strategy, a regional hydraulic fracturing treatment project was implemented in the ultra-high mining height working face, which significantly weakened the pressure relief intensity and achieved ideal results.