深埋隧洞岩爆主动防控作用机制与效果

Mechanism and effects of rockburst active control in deep tunnels

深埋隧洞强岩爆灾害是制约隧道掘进机(tunnel boring machine,TBM)安全高效掘进的关键因素之一,主动防控已成为控制岩爆风险的重要技术手段。该文针对滇中引水工程香炉山深埋隧洞TBM段施工期可能面临的硬岩岩爆问题,在考虑施工因素的情况下,开展超前应力解除爆破和超前导洞数值仿真研究,分析了岩爆主动防控作用机制及不同施工参数下的应力和能量释放效果。结果表明:超前主动防控通过预先集中掌子面前方岩体应力,实现TBM二次开挖时的应力“削峰”,避免能量突然聚集,从而降低岩爆风险;超前应力解除爆破适合局部针对围岩的应力释放,相较于增大外插角,增加超前爆破孔数量对减弱岩爆风险效果更加明显;超前导洞整体应力和能量释放效果更佳,影响范围更大,且增大超前导洞的洞径和长度有助于进一步降低岩爆风险。主动防控方法及具体施工参数需依据实际的岩爆风险等级和现场条件进行确定。

[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 techniques 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.