Mine pressure behavior law and strong mine pressure prevention technology of working face of 10 m super large mining height in Caojiatan Coal Mine

The successful mining of working face of 10 m ultra-large mining height in Caojiatan Coal Mine marks a new stage for the fully-mechanized mining of extra-thick coal seams. Based on multi-source monitoring data, such as mine pressure, displacement and microseismics, the rules of mine pressure behavior and the occurrence mechanism of strong mine pressure in the 10 m ultra-high mining height working face were studied, and a "superimposed arch-beam" structural model of the ultra-high mining height stope was established. A three-in-one surrounding rock control strategy of "active support and protection + regional pressure relief and weakening + all-round monitoring and early warning" was proposed. The results show that the cyclic breaking of the overlying rock in the 10 m ultra-high mining height working face has the characteristics of strong mine pressure, such as strong dynamic load, fast roof sinking speed, long lasting distance of pressure, and high opening rate of support safety valves. The cyclic breaking of the roof of the working face is 10-25 m, the average dynamic load coefficient of periodic pressure is 1.42, and the average maximum shrinkage of support is 0.63 m. During the pressure period, the proportion of hydraulic support safety valves opening rate was more than 50% is 48.1%. The incoming pressure shows regional aggregation characteristics along the tendency direction, distributed in the range of 75-250 m from the nose. The trend direction shows the characteristics of alternating incoming pressure with "large and small cycles", and the average interval between large cycles is 137.5 m. The overlying rock strata of the ultra-high mining face are in a superimposed "arch-beam" structure, and the thick and hard roof in the middle and upper parts overhangs the roof behind the goaf for a long distance, causing the roof to break in front of the face or bend and sink behind the support, causing strong mine pressure appears in face. Reducing the step distance and continuous distance of periodic weighting, reducing the dynamic load coefficient of weighting support, preventing coal wall spalling and avoiding the crushing of hydraulic support are the core elements to control the stability of surrounding rock in 10 m ultra-large mining height working face. The high initial supporting force characteristics of the hydraulic support effectively control the early subsidence of the roof, the high working resistance characteristics relieve the bearing capacity of the coal wall, inhibit the large-area spalling of the coal wall and the rapid subsidence of the roof during pressurization effectively. The double-layer telescopic beam structure of the hydraulic support is combined with the three-level linkage protection device, which realizes the coordinated control of the unsupported area of the roof in front of the support and the protection operation of the ultra-high coal wall, and effectively overcomes the defects of the insufficient protection coverage of the coal wall of the original split protection device. The 5 m³/min high-flow hydraulic fracturing technology, employing a "one-field-one-strategy" zonal parameter design, effectively weakens the thick hard roof, leading to a significant reduction in weighting intervals and dynamic loading coefficients. The real-time warning system of KJ21 mine pressure achieves dynamic monitoring of support operating conditions and roof fracturing.