在既有隧道下方零距离开挖往往导致既有隧道的剧烈扰动，而随着地下空间利用率越来越高，不可避免地出现新旧结构间密贴施工的情况。通过设计合理的施工方案、规范的施工及详尽的监测，能够有效地控制既有结构的变形。依托广州地铁十二号线赤岗站新建站台层密贴下穿既有地铁区间隧道工程，设计了合理的施工方法，并在施工过程中进行了全过程结构监测。结果表明：数值模拟方法预测既有隧道竖向位移及支墩立柱轴力均在安全范围内；现场监测结果表明隧道最大竖向位移达到约6 mm，水平位移保持稳定；轨道沉降差在下穿开挖阶段增大，最大沉降差约4 mm，左右线隧道断面分别内缩4 mm和扩张2 mm，垂直收敛4.5 mm。

Excavation often leads to severe disturbance of the existing tunnels while undercrossing them at zero distance. As the utilization rate of underground space increases, it is inevitable that there will be close fitting construction between new and old structures. By designing reasonable construction plans, standardized construction, and detailed monitoring, the deformation of existing structures can be effectively controlled. Based on the construction of the new platform layer of Guangzhou Metro Line 12 at Chigang station, which underpasses through the existing subway tunnel, a reasonable construction method was designed, and the entire process of structural monitoring was carried out during the construction. The results show that the numerical simulation method predicts that the vertical displacement of the existing tunnel and the axial force of the support column are within the safe range. The on-site monitoring results show that the maximum vertical displacement of the tunnel reaches about 6 mm, and the horizontal displacement remains stable. The settlement difference of the track increases during the excavation stage of the underpass, with a maximum settlement difference of about 4 mm. The cross-section of the left and right tunnel sections shrinks by 4 mm and expands by 2 mm respectively, with a vertical convergence of 4.5 mm.