Stability Analysis of Removal of Steel Supports in Variable-Section Pits
Abstract
1. Introduction
2. Project Overview and Finite Element Model Construction
2.1. Project Overview
2.2. Finite Element Modelling
2.3. Finite Element Model Validation
3. Demolition Support Scheme Design
3.1. Steel Support Numbering
3.2. Layered Backfill and De-Bracing Programme
3.3. Stepped Backfill and De-Bracing Programme
3.4. Supplementary Finite Element Model Analysis Steps for the Disassembly and Bracing Stage
4. Stability Analysis of Layered Backfill and Demolition Support Design Options
4.1. Sedimentation Analysis
4.2. Axial Force Analysis
4.3. Redundancy Analysis
5. Stability Analysis of the Stepped Backfill and Demolition Bracing Design Options
5.1. Sedimentation Analysis
5.2. Axial Force Analysis
5.3. Redundancy Analysis
5.4. Backfilling and De-Bracing Options
6. Conclusions
- Compared with the stepped backfill and split support scheme, the laminar scheme offers more convenience in observing the changing patterns of settlement values and axial forces at different stages, but it is not as good as the stepped scheme in terms of the redundancy of the support structure.
- The redundancy R and relative deformation P effectively reflect the stability of the variable-section pit during each stage of de-bracing. In all five variable-section areas, the minimum redundancy value in the stepped scheme is greater than that in the laminated scheme, with an average increase of 0.03. In addition, the minimum relative deformation is reduced by an average of 5%, with a maximum reduction of 10.52%.
- The stepped removal of braces stabilises the axial force transfer path and controls the range of stress fluctuations, especially during root-by-root removal of steel braces, showing higher redundancy capacity and lower deformation increments. In the lower steel support removal stage, the maximum axial force fluctuation peak value under the stepped solution is only −6.5 MPa, which is smaller than the −8.84 MPa observed in the laminar solution.
- The stepped backfill approach effectively blocks the deformation extension effect between sections and improves the stability of the demolition support in the narrow opening and its distal structural region. In section ①, Pmin increased from −86.9% to −76.38% and Rmin increased to 0.567, which significantly reduced the deformation accumulation effect of the support system.
- The practical significance and engineering value of this study will be further enhanced if scaling experiments on similar models are carried out for validation and analysis in subsequent work.
Author Contributions
Funding
Data Availability Statement
Conflicts of Interest
References
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Soil Layer Name | Density (kg/m3) | Angle of Internal Friction (°) | Cohesion (kPa) | Poisson’s Ratio | Elastic Modulus (MPa) |
---|---|---|---|---|---|
silty clay | 2000 | 20 | 33 | 0.2 | 21.5 |
shale | 2500 | 25 | 50 | 0.2 | 6000 |
conglomerates | 2140 | 28 | 40 | 0.2 | 15,500 |
Makings | Density (kg/m3) | Modulus of Elasticity (MPa) | Poisson’s Ratio |
---|---|---|---|
C15 concrete | 2240 | 22,000 | 0.2 |
C20 concrete | 2360 | 25,500 | 0.2 |
C30 concrete | 2450 | 30,000 | 0.25 |
Q235B steel | 7850 | 200,000 | 0.3 |
No. | Content of the Analysis Step | No. | Content of the Analysis Step |
---|---|---|---|
1 | Ground stress equilibrium | 11 | Step 5 Excavation |
2 | Enclosure construction | 12 | Erection of second and first steel supports for Step 5 |
3 | Step 1 Excavation | 13 | Step 6 Excavation |
4 | Erection of first steel support for Step 1 | 14 | Erection of second and first steel supports for Step 6 |
5 | Step 2 Excavation | 15 | Step 7 Excavation |
6 | Erection of first steel support for Step 2 | 16 | Erection of second and first steel supports for Step 7 |
7 | Step 3 Excavation | 17 | Step 8 Excavation |
8 | Erection of second and first steel supports for Step 3 | 18 | Step 9 Excavation |
9 | Step 4 Excavation | 19 * | Step 10 Excavation |
10 | Erection of second and first steel supports for Step 4 |
No. | Analysis Step | No. | Analysis Step | No. | Analysis Step | No. | Analysis Step | No. | Analysis Step | No. | Analysis Step | No. | Analysis Step |
---|---|---|---|---|---|---|---|---|---|---|---|---|---|
20 | HT1 | 27 | C1107 | 34 | C2102 | 41 | C3103 | 48 | C5102 | 55 | C1204 | 62 | C3201 |
21 | C1101 | 28 | C1108 | 35 | C2103 | 42 | C3104 | 49 | C5103 | 56 | C1205 | 63 | C3202 |
22 | C1102 | 29 | C1109 | 36 | C2104 | 43 | C4101 | 50 | C5104 | 57 | C1206 | 64 | C4201 |
23 | C1103 | 30 | C1110 | 37 | C2105 | 44 | C4102 | 51 | HT2 | 58 | C2201 | 65 | C4202 |
24 | C1104 | 31 | C1111 | 38 | C2106 | 45 | C4103 | 52 | C1201 | 59 | C2202 | 66 | C5201 |
25 | C1105 | 32 | C1112 | 39 | C3101 | 46 | C4104 | 53 | C1202 | 60 | C2203 | 67 | C5202 |
26 | C1106 | 33 | C2101 | 40 | C3102 | 47 | C5101 | 54 | C1203 | 61 | C2204 | 68 | HT3 |
No. | Analysis Step | No. | Analysis Step | No. | Analysis Step | No. | Analysis Step | No. | Analysis Step | No. | Analysis Step |
---|---|---|---|---|---|---|---|---|---|---|---|
20 | HT11 | 27 | C1107 | 34 | C2101 | 41 | C3101 | 48 | HT23+32+41 | 55 | C4202 |
21 | C1101 | 28 | C1108 | 35 | C2102+1203 | 42 | C3102+1206 | 49 | C4104+2204 | 56 | C5201 |
22 | C1102 | 29 | HT12+21 | 36 | C2103 | 43 | C3103+2201 | 50 | C5101+3201 | 57 | C5202 |
23 | C1103 | 30 | C1109 | 37 | C2104+1204 | 44 | C3104 | 51 | C5102+3202 | 58 | HT43 |
24 | C1104 | 31 | C1110+1201 | 38 | C2105 | 45 | C4101+2202 | 52 | C5103+4201 | - | - |
25 | C1105 | 32 | C1111 | 39 | HT13+22+31 | 46 | C4102 | 53 | C5104 | - | - |
26 | C1106 | 33 | C1112+1202 | 40 | C2106+1205 | 47 | C4103+2203 | 54 | HT33+42 | - | - |
Variable Cross-Section Area | Scheme for Removal of Steel Support and Layered Backfill | Scheme for Removal of Steel Support and Stepped Backfill | ||
---|---|---|---|---|
Rmin | Pmin | Rmin | Pmin | |
I Constant section | 0.537 | −86.9% | 0.567 | −76.38% |
II Expansion section | 0.573 | −74.59% | 0.588 | −69.96% |
III Constant section | 0.649 | −54.18% | 0.662 | −51.14% |
IV Contraction section | 0.630 | −58.75% | 0.660 | −51.44% |
V Constant section | 0.525 | −90.50% | 0.544 | −83.98% |
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Huang, Q.; Yao, X.; Wu, J.; Fan, X.; Jin, Y.; Zheng, C. Stability Analysis of Removal of Steel Supports in Variable-Section Pits. Buildings 2025, 15, 1903. https://doi.org/10.3390/buildings15111903
Huang Q, Yao X, Wu J, Fan X, Jin Y, Zheng C. Stability Analysis of Removal of Steel Supports in Variable-Section Pits. Buildings. 2025; 15(11):1903. https://doi.org/10.3390/buildings15111903
Chicago/Turabian StyleHuang, Qi, Xinyu Yao, Jingjiang Wu, Xiaohu Fan, Yang Jin, and Chuanfeng Zheng. 2025. "Stability Analysis of Removal of Steel Supports in Variable-Section Pits" Buildings 15, no. 11: 1903. https://doi.org/10.3390/buildings15111903
APA StyleHuang, Q., Yao, X., Wu, J., Fan, X., Jin, Y., & Zheng, C. (2025). Stability Analysis of Removal of Steel Supports in Variable-Section Pits. Buildings, 15(11), 1903. https://doi.org/10.3390/buildings15111903