Research and Engineering Practice of Coupled Unloading and Supporting Prevention Rock Burst Technology of Hard Coal Seams in Ordos Region

Hard coal seams are important geological feature of rockburst in the Ordos region. In response to the poor pressure relief effect of conventional drilling in hard coal seams in the Ordos region, as well as the problems of high-density and multi round pressure relief and support failure, a non equal pressure stress field model for drilling was established. The mechanical analysis of the plastic zone radius in drilling was derived. This analysis revealed how the coal seam strength and drilling diameter affect the pressure relief effect of drilling. A "shallow support and deep pressure relief" hard coal seam unloading support coupling and expanding pressure relief technology was proposed. A 70m comparative industrial test was conducted on site, and the pressure relief and support effect was tested using methods such as coal powder monitoring, coal gun monitoring, stress monitoring, and surrounding rock deformation monitoring. The conclusion was drawn that: (1) The radius of the plastic zone in drilling is primarily influenced by coal seam strength and drilling deformation. The drilling diameter affects the strength of the coal seam. A smaller plastic zone radius is associated with a larger drilling diameter, while a larger plastic zone radius corresponds to a larger diameter as well. However, the increase in pressure relief effect diminishes as the diameter increases. Therefore, simply increasing the drilling diameter cannot indefinitely improve the pressure relief effect. (2) In terms of the pressure relief effect, the amount of coal powder produced in the expanded pressure relief zone has increased by 3.1 times compared to conventional drilling. The "coal cannon" events are concentrated in the 7-14m section of the coal wall, which can significantly release the accumulated elastic energy inside the coal body; After unloading, the peak stress of the coal body decreases, and the recovery rate becomes slower, which has a significant unloading effect on the concentrated static load area. (3) In terms of the support effect, during and after the pressure relief period of borehole expansion, the stress on the roof of the roadway and the anchor cables on the front wall is stable, and the stress on the anchor cables is lower than that of conventional drilling; In the course of the expansion and pressure relief phase, the maximum observed reduction in the lateral movement of the tunnel's two sides was 63%, while the maximum reduction in the vertical movement of the top and bottom plates reached 51%. The efficacy of this method in mitigating the deformation of the surrounding rock in the tunnel significantly surpasses that achieved through traditional large-diameter drilling techniques. (4) We have developed a complete set of anti-erosion technology and equipment based on mechanical drilling and pressure relief, forming an engineering demonstration. The research results can provide theoretical basis and engineering reference for mines with similar conditions in the Ordos region. (Fund Project: Project supported and financed by the Shaanxi Provincial Natural Science Foundation (Grant No. 2024JC-YBMS-261); Corresponding author: DING Zi-wei; Corresponding author at: Xi 'an University of Science and Technology, Xi 'an, Shaanxi 710054, China. Tel: +86 13991812828. Email address of the corresponding author: zwding@xust.edu.cn.)