324 (a) Horizon diagram of borehole layout (b) Plan view of borehole layout Figure 10 Regional fracturing borehole layout plan for the 10m ultra-large mining height face 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 non-fractured 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
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