Study on the offset law of gas extraction drill holes of soft rock and large deformation coal seam group

With the rapid economic development, China has made remarkable achievements in tunnel construction but is also facing increasing challenges. Among these, the problem of gas outburst, which occurs when tunnels pass through gas-bearing strata, has a larger impact range, higher probability of occurrence, and stronger destructive power, making it more difficult to handle. Gas drainage is the key method to address gas outbursts, but the issue of borehole trajectory deviation is common during the drilling process. To address this, a gas drainage borehole test was conducted at the Zhaotong Tunnel using hydraulic and pneumatic flushing methods. First, by analyzing the theoretical and actual borehole depths, the reliability of the theoretical depth calculation method was verified. Then, two test holes with the smallest errors were selected for trajectory deviation analysis, revealing the deviation pattern of gas drainage borehole trajectories in this tunnel, providing a theoretical basis for subsequent construction. Finally, based on the analysis of hole-forming effects and efficiency, it was concluded that pneumatic flushing method has better applicability.