在地面建筑设施密集的城市进行地铁隧道施工，必然会引起地层移动和变形，对周边及上部既有建筑物造成不利影响，引起隧道上部及临近建筑发生不均匀沉降及开裂，直接影响结构安全。为此，本文针对隧道开挖对上部既有建筑物的影响及加固方法进行研究分析。 本文分析了地铁隧道开挖后上部土层的变形分布规律，提出对地铁隧道开挖引起上部既有建筑物发生沉降采用基础下预压桩基础托换法，并结合西安某学校宿舍楼沉降开裂加固处理项目，应用MIDAS GTS有限元计算分析软件对宿舍楼沉降加固的受力及变形进行数值模拟计算分析，得出四点研究结论：①上部既有建筑物加固前后，地铁隧道上部土体沉降均呈正态分布，最大沉降发生在隧道中心上部；②采用预压托换桩托换法加固后，隧道周围土体及上部既有建筑基础沉降均有较大减小，其中上部建筑基础沉降可减小30%；③采用预压托换桩加固法加固后，地铁隧道衬砌结构应力及变形均有微小变化，其中压应力增加0.4%，拉应力减小3.6%，则对隧道结构不会造成安全问题；④根据实际工程加固施工效果检验分析，采用预压托换桩托换法加固后，使宿舍楼的沉降得到控制，墙体裂缝未继续发展，表明预压桩基础托换法加固有效，且隧道顶短桩桩深以10m为宜，即短桩桩底距隧道顶3m－4m为宜。 上述研究成果可为进一步研究地铁隧道对上部既有建筑物的影响及加固处理研究提供参考，也可供类似加固工程设计及施工参考。

Subway tunnel construction in the ground compact city will result in ground movement and deformation, which will lead to adverse influences to the perimeter and the upper buildings. Therefore, this paper research the subway tunnel excavation’s influences on the upper existing buildings and the reinforcement methods. This paper analyzes the deformation distribution of the upper soil after the tunnel excavation, put forward to use the preloading pile underpinning method to reinforce the settlement of the existing buildings caused by the excavation. Combined with a reinforcement project of a school dormitory settlement cracking in Xi'an, MIDAS GTS finite element software were used to analysis the force and the deformation of the dormitory after reinforcement. Four conclusions were drawn: ① After the reinforcement of upper existing buildings, the settlement of the upper soil was normal distributed and the maximum settlement was occurred in the upper center of the tunnel. ② When using preloading pile underpinning reinforcement, the settlement of the soil around the tunnel and the upper existing building foundation are obviously reduced, wherein the settlement of the upper building foundation can be reduced by 30%. ③ After using preloading pile underpinning reinforcement method, the stress and the deformation of the subway tunnel structure were changed lightly. Compressive stress was increased by 0.4% and tensile stress was reduced by 3.6%-that will not cause security problems to the tunnel structure. ④ Based on the tests and analysis of the actual reinforcement construction, it was showed that after the use of preloading pile underpinning reinforcement method, the settlement of the dormitory was under control, the cracking did not continue on the wall. It suggested that the preloading pile underpinning reinforcement method was available. The short pile under the tunnel should be deep to 10m, namely the distance from the bottom of the short pile to the top of the tunnel should be 3m-4m. The research results can provide reference to further study on the influence of the metro tunnel to the upper existing building and the reinforcement research. What’s more, it can be a reference of design and construction for similar reinforcement project.