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通过对3种不同工况条件下新隧道开挖对既有隧道影响的弹塑性数值分析,得出3种工况对既有隧道围岩的应力及位移的影响规律是一致的———均将引起既有结构物特征点下沉、应力降低,但最终围岩的应力及位移量值较小,既有隧道将处于稳定状态。同时因围岩条件较好,加固效果不甚明显,且依据分析得出在交叉口处前后各1~1.5倍洞径范围内新隧道开挖时对既有隧道影响最大,纵向上影响范围在30~40 m。并依据分析建议一般地段采用全断面法开挖,在交叉口处前后各2~3倍洞径范围内,建议采用台阶法开挖,最后根据影响范围提出具体的监控方案,有力地指导设计与施工。
Through the elastic-plastic numerical analysis of the influence of the new tunneling on the existing tunnel under the three different working conditions, it is concluded that the impact of the three conditions on the stress and displacement of the surrounding rock of the existing tunnel is the same --- both Will cause the sinking and stress reduction of the existing structural feature points, but the final value of the surrounding rock is small and the existing tunnel will be in a steady state. At the same time, due to the good surrounding rock conditions, the reinforcement effect is not obvious. Based on the analysis, it is concluded that the new tunnel excavation has the greatest impact on the existing tunnels in the range of 1 ~ 1.5 times the diameter before and after the intersection, 30 ~ 40 m. According to the analysis and suggestion, general section excavation is carried out by general section method. In the range of 2 ~ 3 times before and after the intersection, it is suggested to use step method to excavate. Finally, according to the influence range, a specific monitoring scheme is proposed to effectively guide the design and construction.