323 2) In-seam conventional boreholes: Drilled from the setup room entry, three boreholes E1–E3 were constructed with horizontal spacing of 60 m, inclination of 1°, and horizon height of 4 m. 3) Roof directional boreholes: Eleven boreholes were drilled from chainage 5600 m in the auxiliary haulage roadway, with a borehole diameter of 120 mm, targeting fracturing horizons at 13 m, 30 m, and 80 m. Two boreholes along the face length direction were arranged from chainage 5900 m in the return airway, 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. Single-borehole 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.
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