1562 4.2 Effectiveness of Roof Hydraulic Fracturing Destressing In Caojiatan Coal Mine, the first weighting spans for faces 122106 and 122108 both exceeded 150 m, with minor air blasts felt during weighting. After implementing hydraulic fracturing, the first weighting span for the ultra-large mining height face 122014 was reduced to 49.3 m. The weighting duration distance was 5.75 m, and the proportion of support leg safety valves opening during weighting was 24.81%. Due to roof weakening by hydraulic fracturing, the first weighting intensity was relatively moderate, and no air blast phenomenon occurred. A comparison of weighting intensity between face 122104 (with fracturing) and an adjacent nonfractured face is shown in the table. After fracturing, periodic weighting spans were all less than 25 m, compared to 10–40 m for the non-fractured face, representing a maximum reduction of 37.5%. The average weighting duration distance after fracturing was 8.35 m, compared to 11.5 m for the non-fractured face, a reduction of 27.4%. The average and maximum dynamic load coefficients decreased by 13.3% and 36.0%, respectively. The average support non-pressure maintenance rate decreased by 66.3%. Table 1 Comparison of weighting intensity between the 10m mining height face and adjacent face Indicator Non-fractured Fractured Periodic weighting span/m 10~40 ＜25 Weighting duration distance/m 11.5 8.35 Average dynamic load coefficient 1.66 1.41 Maximum dynamic load coefficient 2.5 1.6 Support non-pressure maintenance rate/% 3.5~28.2 0.7~10 Average support working resistance/kN 15000~18000 13500~17000 The issues of large-area roof hanging and minor air blasts during the initial mining stage of the ultra-large mining height face were resolved. The first weighting span was 49.35 m, with the proportion of support leg safety valves opening being 24.81%. The intensity of strata pressure behavior during periodic weighting was significantly alleviated. The average and maximum retractions of hydraulic support legs decreased by 33.3% and 23.4%, respectively. The proportion of periods with an average dynamic load coefficient greater than 1.5 decreased by 25.6%. Rib spalling was concentrated within 0.2–0.5 m, within a controllable range. The maximum mining height for face 122104 exceeded 9.8 m, with an average mining height of 9.4 m. The highest daily output reached 71.8 kt, the highest monthly output exceeded 1.55 Mt, and the maximum recovery rate reached 95.3%. By real-time adjusting the fracturing plan and implementing roof management measures such as real-time strata pressure monitoring and warning, and support condition management, the issues of strong strata pressure behavior and rib spalling/caving were effectively controlled. Figure 11 Production site of the world's first 10m ultra-large mining height face
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