Surrounding rock control technology of 10 m super large mining height working face in Caojiatan Coal Mine

The 10 m ultra-large mining height of Caojiatan Coal Mine is a world's first in terms of single mining height and mining intensity, and the effective control of surrounding rock in the stope is crucial for safe and efficient mining at the working face. Based on the coal seam occurrence conditions and the mine pressure manifestation characteristics of the mined working face, the difficulties in controlling the surrounding rock during 10m ultra-large mining height mining are clarified, and a trinity surrounding rock control strategy of “active support and protection + regional pressure relief and weakening + comprehensive monitoring and early warning” is proposed, revealing the mechanism of strong mine pressure manifestation at the 10 m ultra-large mining height working face. The research shows that: the occurrence characteristics of multi-layer thick and hard roofs cause abnormally strong mine pressure manifestation at the working face, with large-area hanging roofs during initial mining and significant strong dynamic loading pressure at the working face during normal mining. The keys to controlling the surrounding rock in the 10m ultra-large mining height stope are reducing the pressure step distance, weakening the dynamic loading pressure, preventing rib spalling, and preventing the working face from being crushed by the pressure. The “double-layer telescopic beams + three-stage rib protection” structure of the hydraulic support achieves independent operation for the protection of the empty roof in front of the support and the ultra-high coal wall, solving the problem of incomplete rib protection by the original split-type rib protection. The high initial setting force and high working resistance of the hydraulic support significantly reduce the risk of rib spalling and roof caving at the working face and effectively control the roof subsidence during the pressure period. The underground deep-hole 5.0 m³/min high-flow directional fracturing weakening technology achieves weakening of the multi-layer thick and hard roofs, effectively reducing the intensity of mine pressure at the working face, controlling the amount of rib spalling and significant roof subsidence during the pressure period, and preventing the working face from being crushed by the pressure. Comprehensive monitoring and early warning effectively ensures the support efficiency of the support during mining, realizing real-time tracking of roof fracture and real-time analysis of strong mine pressure. The problems of large-area hanging roofs and small hurricanes during the initial mining of the ultra-large mining height working face have been resolved. The initial pressure step distance is 49.35 m, the pressure duration distance is 5.75 m, and the opening ratio of the safety valve of the support column is 24.81%. The manifestation of mine pressure during the periodic pressure period has been significantly alleviated. The average shrinkage of the hydraulic support column has decreased from 0.48 m to 0.32 m, a decrease of 33.3%, and the maximum shrinkage has decreased from 1.88 m to 1.44 m, a decrease of 23.4%. The proportion of the average dynamic load coefficient of the working face periodic pressure greater than 1.5 has decreased from 39.6% to 14%. During normal production at the working face, rib spalling is within a controllable range, with the amount of rib spalling concentrated at 0.2-0.5 m. The fracture or bending subsidence of the roof in front of the coal wall in areas where the working face is not sufficiently fractured, or under the condition of a long hanging roof, will cause strong mine pressure manifestation at the working face. The research results have important guiding significance for the control of surrounding rock in ultra-large mining height mining.