Research and engineering practice on mechanical reaming for pressure relief and rock burst prevention technology in hard coal seam roadways

Coal seam drilling for pressure relief is one of the most widely adopted measures to mitigate rock bursts. However, conventional drilling methods exhibit limited effectiveness in hard coal seams and may compromise the integrity of roadway support structures. To optimize traditional pressure relief drilling parameters, this study investigated the influence of coal seam strength and borehole diameter on pressure relief efficiency based on elastoplastic mechanics theory. A novel mechanical reaming technology for pressure relief and rock burst prevention in hard coal seams was developed and subjected to field trials. Multiple monitoring techniques were employed to evaluate its performance in terms of both pressure relief and support stability. The conclusion was drawn that: (1) The higher the strength of the coal seam, the smaller the radius of the plastic zone of the borehole; therefore, the pressure relief effect of the borehole in the hard coal seam is poor. After increasing the diameter of the borehole, the radius of the plastic zone increases, but when the diameter of the borehole increases to 300 mm, the increasing trend of the radius of the plastic zone weakens. Thus, only increasing the diameter of the borehole cannot improve the pressure relief effect of the borehole without limit. (2) An innovative hard coal seam pressure relief and anti-impact technology, termed support, deep pressure relief, unloading-support coupling, the elastic energy accumulated in the coal body through a deep large borehole while utilizing a shallow small borehole to maintain the bearing capacity of the support structure, thereby achieving a balance between pressure relief and support. (3) In comparison to conventional drilling areas, the volume of coal seam drilling powder in the mechanical reaming area has increased by 3.1 times, and the number of per meter has risen by 70%, significantly enhancing the pressure relief effect. Additionally, the anchoring force of the roof anchor cable in the mechanical reaming area has decreased by up to 29%, the variation in tension of the anchor cable on the sides has been reduced by up to 51.8%, the convergence of the two sides of the roadway has diminished by up to 63%, the convergence between the roof and floor has decreased by up to 51%, and both the stress on the support structure and the deformation of the surrounding rock have been significantly reduced. These research findings provide a theoretical foundation and technical support for the prevention and control of rock bursts in similar hard coal seam mining roadways.