Mechanism and effects of rockburst active control in deep tunnels
[Objective]Deep tunnels exhibit characteristics such as high ground stress and strong excavation disturbance.Especially in an intact hard rock environment,the original elastic strain energy stored in surrounding rocks is suddenly released due to the unloading effect during excavation,which can easily trigger rockburst disasters.Severe rockbursts pose a great threat to construction personnel and equipment such as tunnel boring machine(TBM),delaying the construction period and causing huge economic losses.Rockburst hazard is one of the key factors that affect the safety and efficiency of TBM excavation in deep tunnels.Active prevention is the most important technical method for controlling rockburst risk and ensuring personnel and equipment safety during construction.[Methods]With the deeply buried TBM section of the Xianglushan Tunnel in the Dianzhong Water Diversion Project as the engineering background,numerical simulations were performed to analyze the mechanisms and effects of two active rockburst control methods:destress blasting and pilot tunnel.A creep damage model with internal variables was employed to simulate the TBM continuous excavation process.Factors influencing the effectiveness of active rockburst control,such as the external insertion angle,number of advance blasting holes,and diameter and length of the pilot tunnel,were considered.The mechanisms of two active rockburst control methods were elucidated,and the release effects and spatiotemporal evolution processes of stress and energy of surrounding rocks under different construction parameters were studied.[Results]The results demonstrated that active control had achieved the stress"peak-shaving"effect during TBM excavation by preconcentrating rock stress,thereby preventing sudden energy accumulation and reducing rockburst risk.Briefly,it had transferred rockburst risk during the secondary excavation to the construction process of destress blasting and pilot tunnel.The active control method and specific excavation parameters could be determined based on the actual rockburst risk level and on-site conditions.Destress blasting was suitable for local targeted stress release,ensuring that high stresses within the length of advanced boreholes are effectively released in a controlled manner.Increasing the number of advance blasting holes was more important for reducing rockburst risk than increasing the external insertion angle.Compared with destress blasting,pilot tunnel could better transfer and reduce the high stress of surrounding rocks and fully release energy from high-energy-storing rock masses.Furthermore,the overall stress and energy release effects demonstrated by pilot tunnel were better,and the technique's impact range was wider than those of destress blasting.Increasing the diameter and length of pilot tunnel could further reduce the risk of rockbursts.In conclusion,the construction of a pilot tunnel was more complex than that of destress blasting,but its stress release effect was generally better.In cases where a tunnel may have faced strong rockburst risk or other ineffective measures,pilot tunnels could be considered for realizing proactive prevention and rockburst control.[Conclusions]These research results can increase our understanding of the mechanism of rockburst prevention and offer a theoretical basis and a reference for rockburst active control and parameter optimization in practical engineering.
deep tunnelrockburstactive controlstress releasepilot tunnel
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