Effects of Foundation Excavation on Metro Tunnels at Different Locations and Performance of Corresponding Reinforcement Measures: A Case of Shenzhen Metro Line 11, China
Abstract
:1. Introduction
2. Project Overview
2.1. Project Introduction
2.2. Foundation Pit Enclosure Structure and Excavation Scheme
3. Numerical Simulation of Overlapping Foundation Pit Excavation
3.1. Computation Model and Boundary Conditions
3.2. Constitutive Model and Model Parameters
3.3. Numerical Modeling Procedure
3.4. Validation of Numerical Models
3.5. Results and Analysis
4. Discussion on the Selection and Performance of Reinforcement Measures
4.1. Analysis of Reinforcement Measures in the Lower Area
4.2. Analysis of Reinforcement Measures in the Lateral Area
5. Conclusions
- (1)
- In this paper, a numerical simulation method is used to analyze the influence of overlapping foundation pit excavation on adjacent tunnels. The deformation characteristics of adjacent tunnels at different locations caused by foundation pit excavation are studied, and the soil reinforcement measures applicable to tunnels at different locations are proposed, respectively. Based on the above analyses, the following conclusions were drawn:
- (2)
- The deformation characteristics of adjacent tunnels caused by foundation pit excavation can be divided into three areas: the settlement zone, the transition zone, and the uplift zone. Firstly, the settlement zone is mainly located in the lateral area of the foundation pit and in a certain shallow buried stratum below the ground surface. The displacement of the tunnel in the settlement zone is relatively significant in both the vertical and horizontal directions. Secondly, the transition zone is mainly located within a certain range below the settlement zone. The displacement of the tunnel in the transition zone is small in the vertical direction but large in the horizontal direction. Finally, the uplift zone is mainly located in the zone below the foundation pit. The displacement of the tunnel in the uplift zone is large in vertical direction, but small in horizontal direction.
- (3)
- In the lower area, the reinforced soil shows a strong integrity, which makes the stress and strain transfer more uniform. The relative tensile deformation in the shape of “vertical ellipse” of the tunnel section is effectively controlled. Moreover, the integrity of soil is stronger under full-area reinforcement, and increasing the thickness of reinforcement can reduce tunnel deformation more effectively. When the reinforcement thickness is increased from 2 m to 10 m, the maximum vertical displacement of the tunnel is reduced by 21.5%. However, the integrity is weaker under the two kinds of strip reinforcement, and increasing the thickness is ineffective in reducing tunnel deformation. When the reinforcement thickness is increased from 2 m to 10 m, the maximum vertical displacement of the tunnel is only reduced by 11.0% and 6.9%, respectively.
- (4)
- In the lateral area, the reinforced soil has a similar effect as the reinforced soil in the lower area, the reinforced soil has a barrier effect, which significantly reduces the horizontal displacement of tunnel in the lateral area. The relative tensile deformation in the shape of “horizontal ellipse” of the tunnel section is effectively controlled. Moreover, compared with the case without reinforcement, the maximum horizontal displacement decreases by 30.8% and 38.1%, respectively, when the full-area reinforcement thickness is 2 m and 4 m.
- (5)
- The conclusions in this paper are drawn without considering groundwater, so they are applicable to practical projects without groundwater and can also provide a guideline for similar projects. Subsequent research can be carried out around the influence of groundwater and the refinement of soil layers.
Author Contributions
Funding
Institutional Review Board Statement
Informed Consent Statement
Data Availability Statement
Acknowledgments
Conflicts of Interest
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Elastic Modulus E (MPa) | Poisson’s Ratio ν | Cohesion C (KPa) | Friction Angle φ (°) | Unit Weight γ (KN/m3) | |
---|---|---|---|---|---|
Soil | 84 | 0.26 | 29 | 28 | 20 |
Reinforced soil | 100 | 0.25 | / | / | 25 |
Segments | 34,500 | 0.2 | / | / | 25 |
Enclosure structure | 25,000 | 0.2 | / | / | 25 |
Lateral support | 30,000 | 0.2 | / | / | 25 |
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Zhou, Z.; Zhou, Y.; Zhang, H.; Chen, S.; Xiang, L.; Wang, L. Effects of Foundation Excavation on Metro Tunnels at Different Locations and Performance of Corresponding Reinforcement Measures: A Case of Shenzhen Metro Line 11, China. Symmetry 2022, 14, 2561. https://doi.org/10.3390/sym14122561
Zhou Z, Zhou Y, Zhang H, Chen S, Xiang L, Wang L. Effects of Foundation Excavation on Metro Tunnels at Different Locations and Performance of Corresponding Reinforcement Measures: A Case of Shenzhen Metro Line 11, China. Symmetry. 2022; 14(12):2561. https://doi.org/10.3390/sym14122561
Chicago/Turabian StyleZhou, Zelin, Yunlei Zhou, Heng Zhang, Shougen Chen, Long Xiang, and Lu Wang. 2022. "Effects of Foundation Excavation on Metro Tunnels at Different Locations and Performance of Corresponding Reinforcement Measures: A Case of Shenzhen Metro Line 11, China" Symmetry 14, no. 12: 2561. https://doi.org/10.3390/sym14122561