Numerical Simulation Study on the Impact of Deep Foundation Pit Excavation on Adjacent Rail Transit Structures—A Case Study

Urbanization and population concentration in China’s major cities drive high land utilization demands, affecting nearby bridges during underground construction. Foundation pit construction alters the internal forces, deformation, and displacement of bridge piles. To understand these impacts and assess excavation support rationality, a case study was conducted on an ultra-deep foundation pit near an elevated ring road bridge in Wuhan. Considering the engineering geological conditions of the project site, construction sequence, and traffic load on the bridge, a three-dimensional finite element model was established to simulate the impact of foundation pit excavation on the elevated structure. And through an analysis of tracked monitoring data from the construction site, comparisons were also made with the simulation results. The findings of this case study indicated that throughout the entire construction phase of the foundation pit, the maximum horizontal and vertical displacements of the bridge foundation structure caused by the construction are 2.98 mm and −1.75 mm, respectively; the maximum change rate of the bending moment in the bridge structure due to the foundation pit construction is 6.3%, while the change in the axial forces is small, and completely within the safety control standards for bridge structure displacement. By analyzing the monitoring data over three stages within one year after the completion of the foundation pit, it is shown that the bridge structure gradually tends to stabilize. Additionally, due to soil consolidation, its displacement shows uniform rebound and tends to stabilize. The research findings provide valuable reference points for the design and construction of similar deep foundation pit projects.

Study on the Impact of Deep Foundation Pit Construction on Nearby Elevated Structures—Case Study

Huang,

Yan,

Guo

et al. 2024

Impact of Excavation on Adjacent Elevated Bridges and Optimization Analysis of Deformation Control

Wu,

Yu,

Fang

et al. 2024

Based on the deep foundation pit project of the TOD (Transit-Oriented Development) complex of the Shaoxing North High-speed Railway Station, the influence of different construction stages on the deformation and inclination rate of the adjacent elevated bridge and its variation law are studied through field measurement and numerical simulation. The construction process is optimized by the method of reinforcement outside the pit and adjustment of preloaded axial force, and the influence of distance on elevated bridges is summarized. The results show that with the excavation of the foundation pit, the deformation of the bridge pier and bridge pile foundation gradually increases, and the deformation of the bridge piers is larger than that of the bridge pile foundations. As the depth of soil reinforcement outside the pit and the preloaded axial force increases, the maximum vertical displacement of the bridge pier and bridge pile foundations gradually decreases. The deeper the depth of soil reinforcement, the better the displacement control effect on the elevated bridge. In actual construction, it is recommended that the depth of reinforcement be taken as the excavation depth of the pit. It is obvious that the preloaded axial force is subject to the pit angle effect, and the appropriate value of the preloaded axial force should be selected according to the site conditions. The deformation of the bridge pier and bridge pile foundation generally shows a decreasing trend with the increase in the distance between the elevated bridge and the foundation pit. When the elevated bridge is close to the foundation pit, it will be affected by the pit angle effect, and the fluctuation will decrease. The conclusions drawn in the article can serve as the basis and reference for design and construction, and provide reference for similar projects.

Research on Coordinated Relationship Between Deformation and Force in Shaft Foundation Pit Support Structures

Xu,

Hou,

Liu

et al. 2024

In order to investigate the coordinated relationship between lateral deformation of the diaphragm wall and axial force of the internal strut, this paper first carried out a scaled model test on the mechanical features of a foundation pit support system based on a novel axial force servo device. Then, a finite element model was established to simulate the scaled model test, and the correctness of the finite element modeling approach was validated by comparing test results. After that, the same finite element modeling method was used to analyze the coordinated relationship between axial force and lateral deformation in the prototype foundation pit support structure. The results show that the axial force of the inner strut is negatively correlated with the lateral deformation in the diaphragm wall. The initial maximum lateral deformation in the diaphragm wall of the shaft foundation pit occurs at the bottom of the foundation pit, so changing the length of bottom strut simultaneously is the most effective way to adjust the mechanical behavior of the support structure. Under various support conditions, the maximum lateral deformation of the diaphragm wall in the prototype project is 0.59~0.66‰ of the total excavation depth of the foundation pit, and the maximum axial force of internal support is 11~30% of the yield load of a single steel strut.