将既有人防洞改扩建成地铁区间是地下工程的难点和热点之一。哈尔滨地铁项目进场后就遇到了一段已经改建成地下四层沉箱结构的既有人防隧道。如何在确保安全，又不影响正常使用的情况下将该段隧道进行改造托换，是哈尔滨地跌迫切需要解决的难题。为此，哈尔滨地铁项目开展了科技攻关。首先针对地下商场改造托换过程中的荷载分布、结构受力及变形等特点建立数据模型，并进行计算分析。根据模型的结构受力和变形情况及地下商场托换改造结构分析，制定一套安全、有效的结构托换改造方案和监控量测方案，并付之实施，验证了地下商场托换改造结构分析的准确性和施工方案的可操作性，确保了该托换改造施工的安全、可控。

Turning existing civil air defense tunnels into Metro tunnels is one of the focus and difficulties in the field of underground works. During the construction of Harbin Metro, an existing civil air defense tunnel, which has already been turned into a 4floor commercial mall of caisson structure, has to be renovated into a Metro tunnel under the condition that the safety and normal operation of the commercial mall are guaranteed. In the paper, numerical simulation models are established on basis of the load distribution, structure stress and deformation of the underpinning section, and relevant calculations and analysis are made. Then, a series of safe and effective underpinning program and deformation monitoring program are prepared on basis of the stress and deformation of the underpinning section and the analysis results. The construction practice shows that the analysis made is accurate, the construction program prepared is reliable, and the safety of the underpinning construction is guaranteed.