Key technologies for large diameter and long distance through holes drilling in coal mines

The large-diameter and long-distance drilling in coal mines can serve as a transportation channel to replace traditional underground tunnels. Compared with conventional large-diameter drilling, the main differences and difficulties lie in “point-to-point” precise drilling, efficient and rapid reaming of large-diameter and long-distance classification, and full hole section casing laying and grouting for pipe fixation. This article introduces the key technology for drilling holes through large-diameter and long-distance boreholes in coal mines. We will conduct in-depth research on five aspects, including RMRS obstacle avoidance and docking technology, graded hole reaming technology, slag removal process technology, full hole section casing laying technology, and grouting and pipe fixing technology, in order to achieve efficient drilling of large-diameter and long-distance through holes. In the guide straight holes drilled at multiple key points of the drilling design direction track, RMRS technology is used for advanced guidance to achieve directional obstacle avoidance and precise point-to-point penetration; reasonably optimize the drilling sequence and adopt the back pull drilling process to improve the efficiency of drilling; utilizing the combined slag removal process of “intra hole circulation + mechanical assistance” to improve the slag removal efficiency of borehole drilling; optional ball centralizer, using a combination of “forward pull + backward push” to achieve long-distance full hole section casing laying; adopting the “annular pressure grouting method” to ensure the quality of grouting and pipe fixation. Based on the above key technologies, a large-diameter long-distance water transmission pipeline was constructed between Daliuta Well and Huojitu Well, with a total length of 1 932 m, a final borehole diameter of 330 mm, and a water transmission casing size for the entire borehole section ϕ219 mm×8.94 mm; the pilot hole successfully passed diagonally and safely between two bridge piers. The horizontal projection displacement deviation between the actual penetration point Bs and the design penetration point B was 0.4 m, the vertical profile displacement deviation was 0.25 m, and the spatial displacement deviation was 0.47 m, basically achieving point-to-point connectivity; the qualification rate of acoustic amplitude logging for grouting pipes is 95%, and the actual water delivery capacity of the pipeline exceeds 150 m3/h.