Optimization and energy consumption analyses of the support system of a super large deep foundation pit in the Xi'an Metro

The goal of this study is to promote the development of high-quality energy and emission reduction measures for super large deep foundation pits applied in metro system construction projects in areas with loess. In this paper, Rhinoceros 6 is first used to model the super large deep foundation pit on both sides of the existing subway. Second, the Mohr‒Coulomb model and the elastic model are used for numerical calculations in FLAC 3D. In-depth analysis of the deformation of the foundation pit and its surrounding environment and optimization of the support system are performed from the perspectives of safety, economy and environmental protection. Finally, the emission factor method is used to analyze the energy consumption level of the support system. The results reveal that the surface settlement, horizontal displacement of support structure, and horizontal and vertical displacements of the lining increase with the number of construction stages (CONS). In addition, there are strong and stable areas of ground settlement. The ground settlement in the strong area exhibits a V-shaped trend. The horizontal displacement of the lining structure is concentrated in the lower 1/5 of the lining structure, and the vertical displacement gradually decreases from the center toward the east and west. Increases in the pile diameter and diagonal steel support stiffness significantly reduce the deformation of the super large deep foundation pit excavation on its sidewalls and surroundings. The optimized support system greatly reduces the project cost and construction difficulty, and the total carbon emissions are reduced by 27.52%.