Abstract: Based on the second phase project of Nanjing Deji square, this paper introduces the design and practice of deep foundation pit engineering combining the topdown method for the annex building and ordinary excavation method for main building, and summarizes the key technologies and countermeasures of the combination of the topdown method for the annex building and ordinary excavation method for main building. The results monitoring show that the combination of the topdown method and ordinary excavation method greatly accelerates the construction progress of the annex building, achieves the established construction goal, effectively protects the surrounding environment, saves social resources, and achieves good social benefits, which can provide reference for similar projects.

Key words: underground space development, deep foundation pit, the topdown method, one column with one pile, changement of shear wall structures