为解决四线叠交小间距隧道下穿老旧桥梁的沉降控制问题，依托南宁市轨道交通1、2号线区间叠交隧道下穿老旧朝阳溪桥工程，通过数值模拟对朝阳溪桥的变形沉降及管片内力变化规律进行研究，并通过监测数据验证数值模拟及加固措施的有效性。针对实际工程特点，提出钢板围堰导流、旋喷桩加固河床、袖阀管加固桩基、临时支撑系统以及盾构掘进参数控制的措施，确保四线叠交小间距盾构隧道安全下穿朝阳溪桥。研究结果表明： 1）未采取措施前，四线叠交隧道掘进将对桥梁的稳定性造成较大影响，桥梁基础严重倾斜，且会造成隧道管片压溃； 2）朝阳溪桥年代较久，受力结构体系复杂，对地层扰动敏感，应对朝阳溪桥基础进行包裹式注浆加固及旋喷桩+混凝土板护底的河床硬化，确保超浅埋四线盾构隧道安全通过朝阳溪桥，同时防止河流冲刷引起隧道上方覆土流失。

The bridge settlement induced by undercrossing of fourline overlapping smallspacing tunnels should be controlled. As a result, the numerical simulation is adopted to study the deformation settlement of Chaoyangxi Bridge and internal force variation of overlapping tunnels on Nanning Rail Transit Lines 1 and 2. And then the effectiveness of the numerical simulation and reinforcement measures is verified by monitoring data. Finally, the measures of steel cofferdam diversion, rotary jet pile reinforcement for riverbed, Soletanche reinforcement for pile foundation, temporary support system and shield tunneling parameters control are put forward to ensure the safe construction of fourline parallel shield tunnels with small spacing crossing underneath Chaoyangxi Bridge. The results show that: (1) The fourline tunneling will have a great impact on the stability of the bridge if no measures are taken, causing the bridge foundation to tilt seriously and the collapse of some tunnel segments. (2) Chaoyangxi Bridge was built long ago with complex stress structure system and is sensitive to strata disturbance, which indicates that the wrapped grouting reinforcement for bridge foundation and hardening method of the riverbed with rotary jet pile and concrete plate should be carried out to prevent the soil above tunnel from sweeping by river.