以北京地铁某区间盾构下穿既有隧道工程为背景，运用FLAC3D软件对施工过程进行模拟，结合现场实时监测数据对沉降进行分析，并通过对盾构近距离下穿既有线路的整个施工过程进行调查、研究与分析，提出盾构下穿既有隧道沉降控制的有效技术措施。结果表明： 1）设置试验段，根据试验段监测反馈对施工方案进行调整，对穿越段施工有极大的参考意义； 2）适当增大推进土压，提升推进速度，可提高沉降控制效果； 3）设置聚氨脂隔离环和注入克泥效，在沉降控制中起到了十分积极的作用。

In this paper, the construction of a shield tunnel crossing underneath existing Metro tunnel in Beijing is numerically simulated by means of FLAC3D software. Study and analysis are made on the construction of the shield tunnel; and then effective settlement control technologies are proposed. The results show that: 1) The modification of the construction schemes based on data measured can provide effective reference for the shield boring. 2) The settlement control effect can be improved by increasing the shield thrusting force and thrusting speed. 3) The polyurethane isolating ring and “clay short” can obviously improve the settlement control effect.