Optimum Design of Excavation Deepening for Deep Foundation Pits in Complex Sites

Many historical buildings in the old urban area of Zhongshan Road in Guangzhou have high commercial value and requirements for large underground space. However, their safe development is restricted by many factors, such as limited surrounding space, dense underground pipe networks, poor engineering properties of shallow soft soil, and excessive amounts of groundwater. Hence, this work proposes an optimized approach in which the current supporting structure of foundation pits is used for basement expansion in complex environments. A case study of a basement expansion in Honghui Plaza II, Guangzhou, P.R. China, was exemplified in this work. The original foundation pit needed to be deepened to expand the current three-story basement into a four-story one. Although the original diaphragm wall was excavated nearly 10 years ago, it was proved to be suitable for further usage after quality inspection. Thus, together with the partial roof of the basement and steel pipe columns, the diaphragm wall was utilized as a part of the support system. Several measures were taken to avoid deformation risk resulting from short embedded sections. They included structure optimization of the current support system and effective control of the earthwork excavation process. The deformation of the supporting structure and adjacent subway tunnel was simulated using the finite element method during excavation. Results showed that the simulation was basically consistent with the field monitoring value. The excavation deepening of the foundation pit in this case study was proved in practice to have little impact on the surrounding environment. Therefore, the results of this work can serve as a reference for similar urban renewal projects in the future.