Stability of Braced Excavation Underneath Crossing Underground Large Pressurized Pipelines
Abstract
:1. Introduction
2. Project Overview
2.1. The Excavation Project
2.2. Excavation Support System
2.3. Pipeline Suspension Structure
2.4. Geological and Hydrologic Conditions
3. Numerical Modelling
3.1. Finite Element Analysis Software
3.2. Meshing and Boundary Conditions
3.3. Parameters Used for Finite Element Analysis
3.4. Excavation Sequence Simulation
4. Validation of Finite Element Method
5. Results and Discussion
5.1. Deformation Characteristics of Diaphragm Wall and MJS Retaining Wall
5.2. Distribution of Internal Forces in Concrete Strut
5.3. Distribution of Internal Forces in Steel Strut
5.4. Vertical Displacements of Pipelines
5.5. Discussion of Supporting Effect of Pipeline Suspension Structure (PSS)
6. Conclusions
- (1)
- Both the diaphragm wall and the MJS retaining wall have a tendency to deform towards the excavation with proceeding the Excavation Step. The deformation of these walls constantly increases with an increase in the excavation depth.
- (2)
- When the final excavation depth is reached, the distribution of the shear forces in the Y and Z directions along the axis of the concrete strut is in a linear manner, while the distribution of the bending moments in the Y and Z directions is in a symmetric manner.
- (3)
- At the final excavation depth, the shear force in the Y direction is of linear distribution along the axis of the steel strut, and the distribution of the bending moments in both Y and Z directions is almost symmetric with regard to the middle of the steel strut. The magnitude of the maximum shear force in the Z direction is negligible compared to the magnitude of the maximum shear force in the Y direction.
- (4)
- With an increase in the excavation depth, the heave of the pipelines increases due to an increase in the basal heave of the excavation. The maximum heave of pipeline DN1400 is 1 mm greater than that of pipeline DN1800, which may be attributed to the lighter weight of pipeline DN1400.
- (5)
- The installation of the pipeline suspension structure is beneficial for the structural integrity and the safety of the pipelines during both the construction phase and the operational phase of the tunnel. This benefit is obtained by implementing conveniently the operation that the elevation of the pipeline suspension structure cork base is stably lowered during the construction period.
Author Contributions
Funding
Data Availability Statement
Acknowledgments
Conflicts of Interest
References
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Pipeline | Material | Cover Depth (m) | Diameter (m) | Wall Thickness (mm) | Internal Pressure (MPa) |
---|---|---|---|---|---|
DN1800 | steel | 1.45–1.55 | 1.8 | 16 | 0.3 |
DN1400 | steel | 1.60–1.74 | 1.4 | 14 | 0.2 |
Soil Layer Number | Thickness (m) | Unit Weight (kN/m3) | Elasticity Modulus (MPa) | Poisson’s Ratio (-) | Friction Angle (°) | Cohesion (kPa) |
---|---|---|---|---|---|---|
①2 | 1 | 18.5 | 3.5 | 0.23 | 12 | 5 |
①3 | 1.2 | 19 | 4 | 0.2 | 10 | 12 |
③1 | 3.5 | 19.3 | 25 | 0.3 | 16.0 | 33.1 |
③2 | 4.3 | 18.6 | 20 | 0.33 | 17.0 | 19.8 |
④1 | 2 | 18.8 | 22 | 0.36 | 19.2 | 19.6 |
④2 | 1 | 18.4 | 30 | 0.25 | 17.7 | 17.2 |
⑤ | 4 | 18.5 | 20 | 0.33 | 15.9 | 39.4 |
⑥1 | 9.5 | 19.8 | 20 | 0.3 | 18.5 | 17.6 |
Structure | Unit Weight (kN/m3) | Elastic Modulus (MPa) | Poisson’s Ratio (-) | Remark |
---|---|---|---|---|
Diaphragm wall | 25 | 3 × 104 | 0.2 | Thickness = 0.6 m; Depth = 25 m |
MJS wall | 20 | 1 × 104 | 0.2 | From ground surface to −21.4 m |
CISB pile | 20 | 3 × 104 | 0.2 | Diameter = 0.8 m; Length = 30 or 38 m |
Ring beam | 25 | 3 × 104 | 0.2 | Sectional dimension = 1 m × 0.8 m |
Concrete strut | 25 | 3 × 104 | 0.2 | Sectional dimension = 0.8 m × 0.8 m |
Steel strut | 78.5 | 2 × 105 | 0.25 | Diameter = 609 mm; Wall thick. = 16 mm |
Lattice column | 78.5 | 2 × 105 | 0.25 | Longitudinal interval = 6 m |
Cork base | 78.5 | 2 × 105 | 0.25 | Using 32a U-bar |
Fine rolled rebar | 78.5 | 2 × 105 | 0.25 | Diameter = 25 mm |
Monitored Item | Device Used | Version |
---|---|---|
Horizontal disp. at diaphragm wall top | Total station instrument | TCRA1201 |
Vertical disp. at diaphragm wall top | Total station instrument | TCRA1201 |
Pipeline displacements | Total station instrument | TCRA1201 |
Ground surface settlements | Single-point settling meter | YH02-A20 |
Axial forces in struts | Vibrating string-type steel bar meter | GJJ10 |
Groundwater level | Pneumatic water level gauge | YH04-A06 |
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Li, F.; Guo, P.; Geng, N.; Mao, L.; Lin, F.; Zhao, Y.; Lin, H.; Wang, Y. Stability of Braced Excavation Underneath Crossing Underground Large Pressurized Pipelines. Water 2022, 14, 3867. https://doi.org/10.3390/w14233867
Li F, Guo P, Geng N, Mao L, Lin F, Zhao Y, Lin H, Wang Y. Stability of Braced Excavation Underneath Crossing Underground Large Pressurized Pipelines. Water. 2022; 14(23):3867. https://doi.org/10.3390/w14233867
Chicago/Turabian StyleLi, Fangang, Panpan Guo, Ningning Geng, Lei Mao, Feng Lin, Yanlin Zhao, Hang Lin, and Yixian Wang. 2022. "Stability of Braced Excavation Underneath Crossing Underground Large Pressurized Pipelines" Water 14, no. 23: 3867. https://doi.org/10.3390/w14233867
APA StyleLi, F., Guo, P., Geng, N., Mao, L., Lin, F., Zhao, Y., Lin, H., & Wang, Y. (2022). Stability of Braced Excavation Underneath Crossing Underground Large Pressurized Pipelines. Water, 14(23), 3867. https://doi.org/10.3390/w14233867