Simulation study on pressure relief parameters of variable-diameter pressure-relief drilling

Conventional pressure-relief drilling with large diameters causes significant disturbance to shallow surrounding rocks in tunnels, leading to increased support costs. This study focuses on the variable-diameter pressure-relief drilling method and uses theoretical analysis and numerical simulation methods to analyze its pressure-relief mechanism, drilling damage shape, pressure-relief radius, drilling layout, drilling length, and other factors, while comparing the advantages and disadvantages of different drilling schemes. The results show that the use of small-diameter drilling in shallow surrounding rocks can reduce deformation and disturbance, while large-diameter drilling in deep coal seams can provide more space for energy release and achieve better pressure-relief effect. When the vertical stress is greater than the horizontal stress, the drilling damage is in a “butterfly” shape; therefore, the use of double-row three-flower arrangement has the best effect. The length of the small-diameter segment should not exceed the original stress, which is 3 m, and the total length should not exceed the stress concentration zone, which is 25 m. The variable-diameter pressure-relief drilling method can effectively reduce disturbance to shallow surrounding rocks and achieve pressure relief.