以西安南门外综合改造工程环城南路市政隧道上跨既有地铁2号线盾构隧道为依托，根据拟定的设计方案，采用FLAC3D有限差分程序对市政隧道基坑开挖对下卧地铁盾构隧道的影响进行数值分析，并对隧道抗浮进行验算。计算分析结果表明：采用跳槽、分段、分层、对称开挖并结合“板凳桩”加固区间隧道的设计方案能有效控制基底土体的隆起和隧道的变形，盾构隧道变形值和抗浮满足相关保护标准和规范的要求，基坑开挖不会影响地铁2号线的正常安全运营。同时，在施工过程中对区间隧道进行了自动化实时监测，监测结果验证了设计方案的合理性和可行性。设计方案对类似工程的设计和施工具有一定的借鉴和指导意义。

In this article， the influence of the excavation of the foundation pit of Huanchengnanlu municipal tunnel on the existing underlying shieldbored tunnel on No. 2 line of Xi’an Metro is numerically simulated by means of FLAC3D finite differential software， and the antiuplifting of the existing Metro tunnel is calculated. The calculation and analysis result shows that: 1) The uplifting of the soil mass at the bottom of the foundation pit and the deformation of the existing Metro tunnel can be brought under effective control by using alternative， sectionbysection， layerbylayer and symmetrical excavation of the foundation pit and by consolidating the existing Metro tunnel by means of benchshaped piles. 2) The deformation and uplifting of the existing Metro tunnel is within the limits of related standards， and the safe operation of No. 2 line of Xi’an Metro can be guaranteed. Furthermore， automatic realtime monitoring is made for the existing Metro tunnel during the construction of the municipal tunnel and the monitoring result proves that the design of the construction of the municipal tunnel is reasonable and feasible. 