Abstract:

Addressing the complex engineering challenges of a excavated metro station in Chengdu that partially traverses existing buildings, this study adopted a localized undercut and expansion excavation strategy through comprehensive comparative analysis and finite element simulation. The research proposed a scientific method for determining the boundary between open and undercut excavation, and delved into various aspects of key construction technologies such as settlement control, primary support for undercut excavation, and secondary lining, including pre-construction dewatering, ground surface grouting reinforcement, and numerical simulation analysis, as well as advanced support during construction, excavation sequence control, and secondary lining structure construction. The research results indicate that, compared to the traditional open-cut method, the undercut and expansion excavation technique can significantly reduce demolition difficulties, It has significantly cut the investment in project costs by approximately 104 million yuan and shortened the construction period by two months. The key to successful construction lies in accurately determining the boundary between open and undercut excavation, which is recommended to be set outside the structural haunch and 3 m away from the building foundation. Meanwhile, combining sleeve valve pipe ground surface grouting with tube well dewatering measures can effectively control ground surface settlement. During construction, it is necessary to flexibly select construction methods based on the span of the undercut tunnel and the characteristics of surrounding rocks, properly handle the nodes of the primary support structure, ensure effective connection between secondary lining construction and the removal of the primary support structure, and attach great importance to the application of construction monitoring.

Key words: subway, crossing existing buildings, local underground excavation with enlargement, numerical simulation, underground excavation method, open cut method, boundary between underground and open excavation, settlement