Experimental Study on the Weakening Effect and Mechanism of Strainburst by Boreholes with Directional Crack
摘要
Regarding the complex geological and high-stress conditions when deep underground excavation, the combination methods of pressure relief will be the future development trend for minimizing strainbursts. To clarify the weakening effect and mechanism of strainburst by the boreholes with directional crack (BDC) method, this study conducted true-triaxial uploading strainburst experiment by varying boreholes diameter with directional crack. The results show that with the borehole diameters of the specimens increase, the ejection phenomenon of rock fragments gradually decreases, and the negative shear strain and the proportion of shear cracks increases near the BDC area. Compared with intact specimen, the Z axial peak strength and remaining energy of different boreholes diameter specimens all decreases; What’s more, the acoustic emission (AE) energy of the specimens of BDC has obvious early time of rapid growth ahead of peak strength. The weakening mechanism of strainburst by the BDC method is clarified from the perspective of stress relief and energy release. The structural existence of the BDC is equivalent to the prefabricated weak surface, which reduces the rock mass integrity and easily forms the stress relief area. The remaining elastic energy is greatly reduced and the risk of strainburst hazards can be significantly obviously weakened. Based on experiment results, the critical borehole diameter can be suggested to achieve optimum BDC performance. This study provides an effective method for strainburst control when deep underground excavation.
Highlights By conducting the true-triaxial uploading strainburst experiment, the weakening effect of strainburst by the BDC method was verified. The weakening mechanism of strainburst by the BDC method was clarified from two aspects of stress relief and energy release. The critical borehole diameter was suggested to achieve optimum BDC performance.