为了保证基坑工程施工中环境安全和工程安全，控制施工质量，综合考虑土层软弱、地下水丰富及基坑周边环境条件的多样性和复杂性，提出复杂条件下明挖技术“21字”设计施工的基本原则，强调必须坚持“强围护、精控水、快开挖、早支撑、速封闭、勤量测、少扰动”原则和实施信息化动态设计。设计施工要点如下： 1）合理设计围护结构，加强围护结构施工质量； 2）精确控制地下水，包括精准设计控水方案，加强控水措施的施工质量，信息化施工； 3）基坑开挖应体现快速施工，尽快支撑，减少对周边环境的影响； 4）应及时架设支撑，从而减小地表沉降； 5）基坑开挖到坑底后，快速封闭开挖面，并迅速施作结构底板； 6）基坑开挖支护施工中，应加强监控量测，及时采集数据，及时分析，及时反馈，及时指导施工； 7）基坑工程设计和施工过程中，通常要考虑基坑附近地面上作用的荷载，并采取相应的控制措施。通过提出“21字”原则、理念，以提高明挖基坑工程设计和施工水平。

The environmental and engineering safety and construction quality control during foundation pit construction should be guaranteed. As a result, a design and construction method for open excavation technology under complex conditions, i.e. strong retaining, precise water control, fast excavation, early support, fast face closure, frequent measurement and less disturbance, is proposed considering soft strata, rich water and complex surrounding environment. The details of the method include: (1) The retaining structure should be rationally designed, and the construction quality should be strengthened. (2) The groundwater should be precisely controlled, including precise design of water control schemes, strengthening the construction quality of water control measures and informatized construction. (3) The foundation pit should be rapidly excavated to reduce impact on the surrounding environment. (4) The support should be erected in time to reduce ground settlement. (5) The excavation face should be rapidly closed and the structural base should be quickly constructed after the foundation pit is excavated to the bottom. (6) The monitoring and measurement should be strengthened during the excavation and support of foundation pit, and timely data collection, data analysis and feedback should be carried out to guide the construction. (7) The disturbance of ground on foundation pit should be reduced by adopting proper measures. The results can provide reference for design and construction of opencut foundation pits in the future.