Application of beam string steel truss support in a box foundation pit project

With the development of urban underground space to deep and large, green recyclable support technology has become an important development direction of foundation pit engineering. In this paper, the engineering applicability and environmental benefits of the prestressed prefabricated beam string steel truss support technology of a sewage treatment plant in the Guangdong-Hong Kong-Macao Greater Bay Area are systematically demonstrated. By constructing a multi-scheme comparison model of concrete support and beam string steel truss support, combined with finite element numerical simulation and monitoring of the whole construction process, the mechanical properties and deformation control mechanism of the technology are revealed: (1) The prestress control system can realize the active control of foundation pit deformation, and the maximum reverse deformation of some pile top displacement monitoring points is –8.4 mm; (2) The modular assembly technology expands the support spacing from 18 m to 30 m, frees up 30% of the working space, and improves the construction efficiency; (3) A steel-concrete composite support system could effectively solve the problem of plane adaptation of special-shaped foundation pits; (4) The quantitative environmental benefits show that the recycling rate of steel components is more than 95%, reducing construction waste and carbon emissions. This case provides a quantitative design paradigm for green support technology for deep foundation pits, and has practical value for promoting the development of sustainable geotechnical engineering.