1561 targeting a fracturing horizon 5 m above the roof. One borehole was set along the setup room entry axis direction, 20 m above the roof. (a) Plan view of borehole layout (b) Section view of borehole layout Figure 9 Fracturing borehole layout for the initial mining zone of the ultra-large mining height face After the initial mining and caving zone, normal mining proceeded. The layout of roof directional boreholes for the area from chainage 3780 to 5600 m is shown below. This area had 5 fracturing drilling sites. Different fracturing parameters were used in different sections; typical parameter designs are introduced below. 1) Drilling Site F2 (5300 m crosscut): Two fracturing horizons were set: 25 m and 83 m. Six roof directional long boreholes were drilled. Spacing for the 25 m horizon was 99 m, and for the 83 m horizon was 100 m. Single-borehole fracturing interval was 30 m, fracturing duration 90 min, average instantaneous pressure 33 MPa, average flow rate 180 m³/h. 2) Drilling Site F3 (4700 m crosscut): Four fracturing horizons were set: 14 m, 27 m, 55 m, and 80 m. Fifteen roof directional long boreholes (including one horizon detection hole) were drilled. Singleborehole fracturing interval was 50 m, fracturing duration 120 min, average instantaneous pressure 30 MPa, average flow rate 185 m³/h. 3) Drilling Site F4 (4400 m crosscut): Three fracturing horizons were set: 14 m, 34 m, and 55 m. Ten roof directional long boreholes were drilled. Spacing for the 14 m horizon was 60–65 m, for the 34 m horizon was 67 m, and for the 55 m horizon was 100 m. For the 55 m horizon boreholes, the single-borehole fracturing interval was 30 m, fracturing duration 40 min, average instantaneous pressure 18 MPa, average flow rate 160 m³/h. For other horizon boreholes, the single-borehole fracturing interval was 15 m, fracturing duration 40–60 min, average instantaneous pressure 18 MPa, average flow rate 160 m³/h. (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
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