Study on Large Deformation Characteristics and Secondary Lining Supporting Time of Tunnels in Carbonaceous Schist Stratum under High Geo-Stress
Abstract
:1. Introduction
2. Project Description
2.1. Engineering Overview
2.2. Construction Scheme
3. Field Test of Tunnel Deformation Characteristics
3.1. Failure Modes and Cause Analysis
3.2. Layout of Monitoring Points
3.3. Field Test Results
- (1)
- Rapid deformation stage: the excavation of the upper bench to 2~3 days after lower bench excavation. The maximum deformation rates of the three sections are 36.50 mm/d, 34.50 mm/d, and 40.20 mm/d, respectively, and the average deformation rates are 22.41 mm/d, 18.31 mm/d, and 22.60 mm/d, respectively.
- (2)
- Continuous deformation stage: 2~3 days after lower bench excavation to 3~4 days after the inverted arch excavation. The initial support is closed in this stage, and the deformation rate is significantly reduced compared with the rapid deformation stage. However, due to the low strength of the inverted arch at this time, the bearing capacity of the initial support is relatively limited, and the deformation rate is still significant. The average deformation rates of the three sections are 10.13 mm/d, 6.76 mm/d, and 7.54 mm/d, respectively.
- (3)
- Slow deformation stage: after 3~4 days of inverted arch excavation. In this stage, the supporting capacity of the initial support is greatly improved, and the deformation rate is reduced to a negligible level. However, under the influence of unfavorable factors such as the rheological behavior of the surrounding rock, high ground stress, and insufficient support strength, the tunnel still deforms slowly at a specific deformation rate. The average deformation rates of the three sections are 4.04 mm/d, 1.39 mm/d, and 1.92 mm/d, respectively.
4. Supporting Time Analysis of Secondary Lining
4.1. Determination Method of Supporting Time
4.2. Full Displacement Calculation of Tunnel
4.2.1. Test Sections
4.2.2. Test Results
4.2.3. Full Displacement Calculation
4.3. Field Test of Secondary Lining Internal Force
4.4. Secondary Lining Supporting Time
5. Conclusions
- (1)
- In constructing a carbonaceous schist tunnel under high geo-stress, the main failure modes are tunnel face collapse, primary support cracking, steel arch damage, primary support invasion limit, and secondary lining cracking. These failure modes correspond to different construction stages. Among them, steel arch failure and primary support invasion were the most frequently occurring forms of damage. Weak and fragmented strata, high ground stress, and insufficient support strength are the leading causes of large deformations in the tunnel.
- (2)
- When the three-bench method is used for tunnel construction, the peripheral convergence is significantly greater than the vault settlement. The maximum convergence is 629.6 mm, and the maximum settlement is 505 mm. The early deformation is large, and the deformation rate is high. The maximum convergence rate is 40.20 mm/d, and the maximum settlement rate is 32.40 mm/d. Before the middle bench excavation, the deformation accounts for the largest proportion of the total deformation monitored, about 35~41%. From the lower step excavation to the inverted arch excavation, the deformation accounts for about 27% of the total deformation monitored. After the inverted arch excavation, the deformation accounts for the smallest proportion, about 16~23%. There are differences in the lateral convergence deformations of the three bench levels, and the tunnel deformations show significant asymmetry.
- (3)
- The secondary lining is in a state of compression. The inner side of the tunnel vault and inverted arch is mainly subjected to tension, and the force of the remaining positions has no obvious regularity. The maximum bending moment value and the maximum axial force value mainly appear in the tunnel hance and knee, and the maximum bending moment and axial force can reach 298.6 kN·m and 3092.4 kN, respectively. The left tunnel knee is the weak position of the secondary lining, and it should be strengthened during construction.
- (4)
- The optimal secondary lining supporting time can be indirectly characterized by the displacement release rate and structural safety factor. With the increase of the displacement release rate, the minimum safety factor of the secondary lining increases first and then decreases. The minimum safety factor is the largest when the displacement release rate is 90.8%. The displacement release rate corresponding to the optimal supporting time of the secondary lining is 90.8%, and the displacement release rate corresponding to the optimal supporting period is 88~93%.
Author Contributions
Funding
Institutional Review Board Statement
Informed Consent Statement
Data Availability Statement
Conflicts of Interest
References
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Support Type | Item | Support Parameters |
---|---|---|
Initial support | Shotcrete grade | C25 |
Thickness of shotcrete | 27 cm | |
Steel arch type | I20b | |
Spacing of steel arch | 80 cm | |
Bolt type | Arch: φ25 combination hollow bolt Side wall: φ22 mortar bolt | |
Spacing of bolt | 120 cm × 100 cm (circumferential × longitudinal) | |
Length of bolt | 3.5 m | |
Size of steel mesh | φ8 | |
Spacing of steel mesh | 20 cm × 20 cm | |
Secondary lining | Thickness | 50 cm |
Concrete grade | C35 | |
Invert filling | Concrete grade | C20 |
Excavation Step | Middle Bench Excavation | Lower Bench Excavation | Inverted Arch Construction | ||||
---|---|---|---|---|---|---|---|
Section | Vault Settlement | Peripheral Convergence | Vault Settlement | Peripheral Convergence | Vault Settlement | Peripheral Convergence | |
DK354 + 400 | 30.00% | 40.67% | 44.73% | 58.63% | 76.50% | 83.44% | |
DK354 + 430 | 44.10% | 43.24% | 61.99% | 61.88% | 82.40% | 82.69% | |
DK354 + 460 | 30.48% | 39.12% | 43.45% | 50.70% | 73.25% | 86.48% | |
Average value | 34.86% | 41.01% | 50.06% | 57.07% | 77.38% | 84.21% |
Monitoring Section | Regression Equation | Full Displacement/cm |
---|---|---|
Case 1: DK356 + 260 | 26.80 | |
Case 2: DK356 + 270 | 32.30 | |
Case 3: DK356 + 280 | 35.80 | |
Case 4: DK356 + 290 | 34.00 | |
Case 5: DK356 + 300 | 32.40 |
Monitoring Section | Measured Displacement um/cm | Total Displacement before Secondary Lining Construction (u1 + u2 + um)/cm | Displacement Releasing Rate η /% | Minimum Safety Factor |
---|---|---|---|---|
Case 1 | 14.88 | 25.84 | 96.4 | 2.20 |
Case 2 | 16.99 | 29.33 | 90.8 | 5.80 |
Case 3 | 17.20 | 30.36 | 84.8 | 2.41 |
Case 4 | 18.05 | 32.27 | 94.9 | 2.50 |
Case 5 | 16.08 | 28.35 | 87.5 | 3.60 |
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Tan, Y.; Chen, B.; Liu, Z. Study on Large Deformation Characteristics and Secondary Lining Supporting Time of Tunnels in Carbonaceous Schist Stratum under High Geo-Stress. Sustainability 2023, 15, 14278. https://doi.org/10.3390/su151914278
Tan Y, Chen B, Liu Z. Study on Large Deformation Characteristics and Secondary Lining Supporting Time of Tunnels in Carbonaceous Schist Stratum under High Geo-Stress. Sustainability. 2023; 15(19):14278. https://doi.org/10.3390/su151914278
Chicago/Turabian StyleTan, Yinjun, Binke Chen, and Zheng Liu. 2023. "Study on Large Deformation Characteristics and Secondary Lining Supporting Time of Tunnels in Carbonaceous Schist Stratum under High Geo-Stress" Sustainability 15, no. 19: 14278. https://doi.org/10.3390/su151914278