依托南京地铁S8宁天城际下穿宁启铁路工程，结合南京地质条件，一方面研究新建地铁隧道下穿既有铁路线时，地铁隧道施工对既有铁路线的影响；另一方面研究地铁施工时，为后期铁路复线扩建预留施工条件的方案。提出在既有铁路线下方采用注浆加固的方法以规避风险，采用“桩+板”加固的方法预留后期铁路复线施工条件。研究结果表明，采用注浆加固时，地铁隧道双线贯通铁路线路最大沉降（6.9 mm）比不加固减小58.9%，铁路线路最大高低偏差（3 mm），比不加固减小51.3%，采用“桩+板”加固预留铁路复线扩建条件，桩板结构最大变形及内力均能满足规范要求。

A study was carried out to research the settlement of railway foundation caused by construction of shield tunnel, and the influence of expanded railway construction to newly constructed subway tunnel. Put forward to use grouting to reinforce existing railway foundation and use pile + plate to reserve space for construction of expanded railway foundation. The result shows that when the sub way tunnel completed the largest settlement of existing railway foundation is 6.9mm after grouting reinforcement, reducing 58.9% than conducting no measures; the largest line elevation difference is 3mm, reducing 51.3%. On the other hand, the largest deformation and internal force can meet requirement of specification by using pile + plate reinforcement to reserve space for construction of expanded railway foundation.

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