城市地下高速公路隧道下穿既有地铁线过程中，往往导致地铁线和地表发生较大沉降，为研究其沉降规律及控制技术，以智利圣地亚哥城市地下高速公路隧道下穿既有地铁线工程为背景，运用FLAC3D软件，对以侧壁导坑法施工，采用超前支护、无系统锚杆的初期支护、二次衬砌及临时加固相结合支护的施工过程进行仿真模拟，并对既有地铁线及地表的沉降进行分析。结果表明：地表最大沉降为35.9 mm，既有地铁线最大沉降为33.4 mm，横向轨道面最大不均匀沉降率为0.623‰，纵向最大不均匀沉降率为0.27‰，不均匀沉降率小于规定的沉降阈值（1‰），地铁线及地表的沉降量均控制在规范和地铁运营部门要求的范围内，可确保下穿施工期间既有地铁线的结构安全。

The construction of urban underground highway tunnel crossing underneath existing metro lines often causes large settlement of existing metro lines and ground surface; and it is significant to study its settlement regularity and control technology. The construction process of a highway tunnel crossing underneath two existing metro lines in Santiago, Chile, which adopts side heading method combined with advance support, primary support without systemic anchor bolt, secondary lining and temporary support, is simulated by software FLAC3D; and the settlement of the existing metro lines and ground surface is analyzed. The numerical simulation results show that the maximum settlements of ground surface and existing metro lines are 35.9 mm and 33.4 mm, respectively; the maximum differential settlement ratios of transversal and longitudinal rail track plane are 0.623‰ and 0.27‰, respectively, and the differential settlement ratio is less than specified settlement threshold; the settlements of the existing metro lines and ground surface are within the limits of specification and requirement of metro operation department; and the structure safety of existing metro lines can be guaranteed during the urban underground highway tunnel construction.