Effect of Steel Support Cross-Section and Preloaded Axial Force on the Stability of Deep Foundation Pits
Abstract
:1. Introduction
2. Project Overview
3. Numerical Simulation of Deep Foundation Pit
3.1. Geometric Modelling
3.2. Selection of Material Parameters
3.3. Analysis Step Establishment
3.4. Contact and Boundary Condition Settings
3.5. Meshing
3.6. Numerical Model Validation
4. Mechanical Response Analysis of Steel Support in Deep Foundation Pit
4.1. Establishment of Evaluation Indicators
4.2. Effect of Steel Support Cross-Section Size on Pit Stability
4.2.1. Effect of Cross-Section Dimensions on Horizontal Displacements of Enclosures
4.2.2. Effect of Steel Support Cross-Section Size on Axial Force
4.3. Effect of Preloaded Axial Force of Steel Support on the Stability of the Deep Foundation Pit
4.3.1. Effect of Preloaded Axial Force of Steel Support on Horizontal Displacement of Enclosure Structure
4.3.2. Effect of Steel Support Preloaded Axial Force on Surface Settlement
5. Discussion
- (1)
- The diameter and wall thickness of the steel support have a significant effect on both the horizontal displacement and axial force of the enclosure structure. Space constraints and material costs need to be considered comprehensively in the design.
- (2)
- During the excavation and support of the foundation pit, a real-time monitoring system should be set up to monitor key parameters such as surface settlement and axial force of steel support.
- (3)
- During the design and construction process, it is also necessary to comprehensively consider the influence of factors such as the nature of the soil, changes in the water table, and the construction process on the surface settlement. Through multi-factor analysis, a more comprehensive and scientific foundation pit support programme can be developed.
6. Conclusions
- (1)
- As an important part of the deep foundation pit structure, the detailed characteristics of the steel support will affect the safety of the foundation pit, and quantitative evaluation of the effect of the steel support diameter, wall thickness, and preloaded axial force level on the safety of the foundation pit has considerable engineering significance.
- (2)
- Under the same diameter, the horizontal displacement of the enclosing pile changes from 4.64 mm to 13.55 mm as the wall thickness increases from 14 mm to 25 mm, and the axial force of the second steel support decreases by 11.4% to 15% for every 2 mm increase in wall thickness.
- (3)
- When the diameter of the steel support changes from 609 mm to 800 mm, the axial force of the second steel support decreases by 3.2–5.5%. The analysis of the combined effect of steel support diameter and wall thickness indicate that the two have a coupling effect on the safety of the pit; the diameter of the steel support can be reduced and the wall thickness can be increased to achieve the same stabilising effect in special working conditions with space limitations.
- (4)
- Compared with a 60% preloaded axial force level, 120% preloaded axial force can reduce the horizontal displacement of the pile top in the pit by about 10 mm and that of the surface settlement by about 4.2 mm. This finding indicates that the change in the preloaded axial force of the steel support affects the horizontal displacement of the enclosure structure and the surface settlement.
- (5)
- From the perspective of pit safety, the pit can be concluded to be in a safe state when the preloaded axial force level is 60%. Thus, reducing the preloaded axial force level scientifically and reasonably is feasible under the premise of guaranteeing the safety of the pit in the actual construction process.
Author Contributions
Funding
Data Availability Statement
Conflicts of Interest
References
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Soil Layer | Density/(kg/m3) | Internal Friction Angle/° | Cohesive Force/kPa | Poisson’s Ratio | Elastic Modulus/MPa |
---|---|---|---|---|---|
Silty Clay | 2000 | 20 | 33 | 0.25 | 39 |
Mudstone | 2500 | 25 | 50 | 0.25 | 6000 |
Conglomerate | 2140 | 28 | 40 | 0.25 | 11,000 |
Materials | Density/(kg/m3) | Elastic Modulus/MPa | Poisson’s Ratio |
---|---|---|---|
C30 Concrete | 2450 | 30,000 | 0.3 |
Q235B Steel | 7850 | 210,000 | 0.3 |
Step | Analysis Step Content | Step | Analysis Step Content |
---|---|---|---|
1 | Ground Stress Equilibrium | 10 | Erection of The Second Steel Support for Section II and The First Steel Support for Section IV. |
2 | Enclosure Construction | 11 | I Section V, II Section IV, III Section III, IV Section II, V Section I Soil Excavation |
3 | Excavation of The First Layer of Soil in Section I | 12 | Erection of The Second Steel Support for Section III and The First Steel Support for Section V. |
4 | Erection of The First Steel Support for Section I | 13 | II Section V, III Section IV, IV Section III, V Section II Soil Excavation |
5 | Excavation of The Second Layer of Section I and The First Layer of Section II | 14 | Erection of The Second Steel Support for Section IV |
6 | Erection of The First Steel Support for Section II | 15 | Excavation of The Soil in Layer 5 of Section III, Layer 4 of Section IV, Layer 3 of Section V |
7 | Excavation of Soil in Layer 3 of Section I, Layer 2 of Section II, Layer 1 of Section III | 16 | Excavation of Soil in Layer 5 of Section IV and Layer 4 of Section V |
8 | Erection of The First Steel Support for Section III | 17 | Excavation of Soil Layer 5 of Section V |
9 | Excavation of Soil in Layer 4 of Section I, Layer 3 of Section II, Layer 2 of Section III, Layer 1 of Section IV |
Monitoring Projects | Engineering Monitoring Level II | ||
---|---|---|---|
Cumulative Value/mm | Rate of Change/(mm/d) | ||
Absolute Value | Relative Pit Depth (H) Value | ||
Vertical Displacement of Pile Top | 20–30 | 0.15–0.3% | 3–4 |
Horizontal Displacement of Pile Top | 20–30 | 0.15–0.3% | 3–4 |
Horizontal Displacement of Pile Body | 30–40 | 0.2–0.4% | 3–4 |
Surface Settlement | 25–35 | 0.2–0.3% | 2–4 |
Rebounding of Pit Bottom Elevation | 25–35 | 2–3 | |
Supporting Axial Force | Maximum Value: (70–80%) f Minimum Value: (80–100%) fy |
Depths/m | Diameter 609 mm Steel Support Wall Thickness/mm | |||||
---|---|---|---|---|---|---|
12 mm | 14 mm | 16 mm | 18 mm | 20 mm | 25 mm | |
0 | 9.27 | 8.03 | 7.09 | 6.55 | 5.73 | 4.64 |
0.50 | 7.93 | 6.94 | 6.17 | 5.76 | 5.08 | 4.20 |
1.00 | 6.60 | 5.84 | 5.26 | 4.96 | 4.42 | 3.75 |
1.13 | 6.23 | 5.51 | 4.96 | 4.68 | 4.18 | 3.55 |
2.00 | 3.88 | 3.43 | 3.09 | 2.92 | 2.60 | 2.22 |
3.00 | 6.18 | 5.26 | 4.56 | 4.13 | 3.55 | 2.75 |
3.85 | 9.43 | 8.03 | 6.94 | 6.29 | 5.39 | 4.16 |
4.70 | 1.49 | 1.20 | 0.98 | 0.84 | 0.68 | 0.44 |
5.70 | −7.04 | −6.14 | −5.44 | −4.54 | −3.97 | −2.87 |
6.70 | −11.67 | −10.21 | −9.06 | −7.58 | −6.65 | −4.83 |
7.47 | −13.46 | −11.83 | −10.55 | −8.85 | −7.80 | −5.72 |
8.24 | −14.57 | −12.86 | −11.51 | −9.70 | −8.58 | −6.34 |
9.20 | −15.46 | −13.71 | −12.33 | −10.43 | −9.26 | −6.90 |
10.15 | −15.91 | −14.17 | −12.78 | −10.85 | −9.66 | −7.24 |
11.11 | −16.08 | −14.36 | −12.99 | −11.06 | −9.87 | −7.44 |
12.07 | −15.90 | −14.24 | −12.92 | −11.02 | −9.85 | −7.46 |
12.95 | −15.25 | −13.69 | −12.44 | −10.63 | −9.52 | −7.23 |
13.84 | −13.69 | −12.31 | −11.21 | −9.59 | −8.60 | −6.54 |
14.73 | −10.67 | −9.60 | −8.75 | −7.49 | −6.72 | −5.12 |
15.62 | −6.65 | −5.99 | −5.46 | −4.67 | −4.19 | −3.20 |
16.50 | −5.42 | −4.88 | −4.44 | −3.80 | −3.41 | −2.59 |
Depths/m | Diameter 800 mm Steel Support Wall Thickness/mm | |||||
---|---|---|---|---|---|---|
12 mm | 14 mm | 16 mm | 18 mm | 20 mm | 25 mm | |
0 | 8.57 | 7.42 | 6.38 | 5.42 | 4.52 | 3.54 |
0.50 | 7.52 | 6.59 | 5.73 | 4.91 | 4.14 | 3.32 |
1.00 | 6.47 | 5.75 | 5.06 | 4.40 | 3.75 | 3.09 |
1.13 | 6.12 | 5.44 | 4.79 | 4.16 | 3.55 | 2.92 |
2.00 | 3.85 | 3.42 | 3.01 | 2.62 | 2.23 | 1.84 |
3.00 | 5.60 | 4.73 | 3.97 | 3.29 | 2.68 | 1.99 |
3.85 | 8.51 | 7.18 | 6.01 | 4.97 | 4.04 | 2.99 |
4.702 | 1.22 | 0.95 | 0.73 | 0.56 | 0.41 | 0.24 |
5.70 | −6.66 | −5.79 | −4.98 | −3.81 | −3.19 | −2.23 |
6.70 | −11.10 | −9.68 | −8.37 | −6.42 | −5.38 | −3.80 |
7.47 | −12.91 | −11.32 | −9.84 | −7.59 | −6.38 | −4.55 |
8.24 | −14.09 | −12.42 | −10.83 | −8.39 | −7.09 | −5.09 |
9.20 | −15.08 | −13.36 | −11.72 | −9.12 | −7.73 | −5.60 |
10.15 | −15.63 | −13.91 | −12.25 | −9.56 | −8.14 | −5.94 |
11.11 | −15.88 | −14.18 | −12.53 | −9.81 | −8.37 | −6.13 |
12.07 | −15.78 | −14.13 | −12.51 | −9.82 | −8.39 | −6.18 |
12.95 | −15.18 | −13.63 | −12.09 | −9.50 | −8.13 | −6.00 |
13.84 | −13.67 | −12.29 | −10.91 | −8.59 | −7.36 | −5.44 |
14.73 | −10.67 | −9.60 | −8.54 | −6.72 | −5.76 | −4.27 |
15.62 | −6.65 | −5.99 | −5.32 | −4.19 | −3.59 | −2.66 |
16.50 | −5.42 | −4.87 | −4.32 | −3.40 | −2.91 | −2.15 |
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Jin, Y.; Zhao, H.; Zheng, C.; Liu, J.; Ding, C. Effect of Steel Support Cross-Section and Preloaded Axial Force on the Stability of Deep Foundation Pits. Buildings 2024, 14, 2532. https://doi.org/10.3390/buildings14082532
Jin Y, Zhao H, Zheng C, Liu J, Ding C. Effect of Steel Support Cross-Section and Preloaded Axial Force on the Stability of Deep Foundation Pits. Buildings. 2024; 14(8):2532. https://doi.org/10.3390/buildings14082532
Chicago/Turabian StyleJin, Yang, Hanzhe Zhao, Chuanfeng Zheng, Jian Liu, and Chong Ding. 2024. "Effect of Steel Support Cross-Section and Preloaded Axial Force on the Stability of Deep Foundation Pits" Buildings 14, no. 8: 2532. https://doi.org/10.3390/buildings14082532