Design of Tunnel Initial Support in Silty Clay Stratum Based on the Convergence-Confinement Method
Abstract
:1. Introduction
2. Engineering Survey
3. Determination of the Key Curves of CCM
3.1. Ground Reaction Curve
3.2. Longitudinal Displacement Profile
3.3. Support Characteristic Curve
- (a)
- Steel grille acts as support alone:
- (b)
- Steel grid and spray concrete are combined to support:
4. Support Scheme Design
4.1. Safety Factor of the Permitted Displacement
4.2. Optimization of Supporting Time
5. Discussion
6. Conclusions
- (1)
- The stress release ratio of the surrounding rock in the silty clay stratum is approximately 78–90% when the supporting structure and surrounding rock displacement are coordinated and stable under the current excavation and support conditions. The surrounding rock displacement began at one time diameter of the tunnel in front of the tunnel face. Under the condition of subgrade V in the silty clay stratum, the displacement before installing the supporting structure is approximately 33.28 mm, which belongs to the nonmonitorable portion, accounting for 64% of the total displacement of the surrounding rock. After installation of the supporting structure, the coordinated displacement is approximately 18.45 mm, which belongs to the monitorable portion, accounting for 36% of the total displacement.
- (2)
- Based on the convergence–confinement method, the longitudinal displacement law of silty clay under different subgrade conditions is determined by the hyperbolic tangent function. Then, the stress release law and displacement law of the surrounding rock under support are further determined. In the existing supporting design, the permitted displacement is 16.31 mm, and the maximum supporting force is 0.221 MPa when the steel grid support alone. The permitted displacement is 25.63 mm, and the maximum supporting force is 1.897 MPa for the combined support of the steel grid and spray concrete.
- (3)
- For the condition of subgrade V in a silty clay stratum, the safety factor of the permitted displacement is approximately 2.91, which can ensure tunneling stability. It is suggested that initial support should be carried out within 1 m after face advancement. For the surrounding rock of subgrade VI1, the safety factor of the permitted displacement is 1.40. The initial support must be carried out 1 m ahead of the tunnel face. Therefore, it is suggested to adopt advanced small conduits to ensure the safety and quality of construction. For the condition of subgrade VI2, the surrounding rock must be supported 4 m ahead of the tunnel face, and the advanced pipe shed or deep hole grouting reinforcement can be considered. The treatment effect of the relevant schemes still needs to be further studied.
Author Contributions
Funding
Institutional Review Board Statement
Informed Consent Statement
Data Availability Statement
Conflicts of Interest
References
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Parameters | Void Ratio, e | Density, G (cm3) | Water Content, w (%) | Plastic Limit, wP (%) | Liquid Index, IL | Cohesion, cs (kPa) | Friction Angle, φs (°) | Poisson’s Ratio, μs | Young Modulus, Es (MPa) | |
---|---|---|---|---|---|---|---|---|---|---|
Subgrade | ||||||||||
V | 0.6–0.7 | 1.95 | 21–24 | 18.5–22.4 | 0.05–0.25 | 40 | 20 | 0.33–0.35 | 80 | |
VI1 | 0.7–0.8 | 1.90 | 24–29 | 0.25–0.75 | 25 | 19 | 0.35–0.38 | 50 | ||
VI2 | 0.8–0.9 | 1.85 | 30–34 | 0.75–1 | 20 | 18 | 0.38–0.43 | 30 |
Subgrade | a1 | b1 | S0 (m) | SSE | R2 |
---|---|---|---|---|---|
V | 1.720 | 3.028 | 0.136 | 1.53 × 10−6 | 0.9999 |
VI1 | 1.983 | 4.708 | 0.832 | 0.0045 | 0.9993 |
VI2 | 2.118 | 5.448 | 5.543 | 0.3667 | 0.9990 |
Section Number | Initial Measurement Time, (d) | Measured Final Value, (mm) | a2 | b2 | (mm) | (mm) | SSE | R2 |
---|---|---|---|---|---|---|---|---|
① | 1 | 6.565 | 0.1701 | –6.794 | 9.581 | 16.146 | 7.88 × 10−6 | 0.9362 |
② | 1 | 6.225 | 0.2118 | –9.956 | 8.972 | 15.197 | 2.52 × 10−5 | 0.8353 |
③ | 3 | 6.352 | 0.1781 | –1.069 | 8.762 | 15.114 | 9.27 × 10−6 | 0.8841 |
④ | 3 | 6.671 | 0.1954 | –2.123 | 9.461 | 16.132 | 5.07 × 10−6 | 0.9377 |
⑤ | 3 | 5.553 | 0.1613 | –5.499 | 9.854 | 15.407 | 5.52 × 10−6 | 0.9099 |
⑥ | 1 | 6.567 | 0.1029 | –6.732 | 8.673 | 15.240 | 8.58 × 10−6 | 0.8952 |
⑦ | 2 | 5.547 | 0.1519 | –7.291 | 8.965 | 14.512 | 4.86 × 10−5 | 0.8136 |
⑧ | 2 | 6.894 | 0.1551 | –7.982 | 8.423 | 15.317 | 8.95 × 10−5 | 0.8566 |
Average value | - | 6.297 | 0.1658 | –5.931 | 9.086 | 15.383 | - | - |
Section Number | Position 1# | Position 2# | Position 3# | Position 4# | Position 5# | Average Value |
---|---|---|---|---|---|---|
① | 0.035 | 0.036 | 0.089 | 0.034 | 0.074 | 0.0536 |
② | 0.063 | 0.066 | 0.113 | 0.161 | 0.108 | 0.1022 |
③ | 0.044 | 0.129 | 0.212 | 0.073 | 0.076 | 0.1068 |
④ | 0.108 | 0.133 | 0.09 | 0.094 | 0.072 | 0.0994 |
⑤ | 0.103 | 0.021 | 0.05 | 0.104 | 0.095 | 0.0746 |
⑥ | 0.028 | 0.084 | 0.065 | 0.027 | 0.026 | 0.046 |
⑦ | 0.086 | 0.066 | 0.077 | 0.022 | 0.028 | 0.0558 |
⑧ | 0.029 | 0.062 | 0.047 | 0.074 | 0.034 | 0.0492 |
Steel Grid | Spray Concrete | ||||||||
---|---|---|---|---|---|---|---|---|---|
Eseq/GPa | As/cm2 | Is/m4 | σs′/MPa | tseq/m | Ec/GPa | μc | tc/cm | Leqc/(GPa) | Pmc/MPa |
1.52 | 15 | 9.78 × 10−6 | 2.92 | 0.28 | 20 | 0.2 | 25 | 0.52 | 1.85 |
Support Form | Support Stiffness (GPa) | Permitted Displacement (mm) | Maximum Support Force (MPa) |
---|---|---|---|
Steel grid | 0.0440 | 16.31 | 0.221 |
Steel grid-spray concrete | 0.5845 | 25.63 | 1.897 |
Subgrade | umax (mm) | uin (mm) | ueq (mm) | Fs |
---|---|---|---|---|
V | 87 | 33.28 | 51.73 | 2.91 |
VI1 | 100 * | 74.14 | 92.59 | 1.40 |
VI2 | 100 * | 271.60 | 290.05 | <1 |
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Liu, K.; Zhao, W.; Li, J.; Ding, W. Design of Tunnel Initial Support in Silty Clay Stratum Based on the Convergence-Confinement Method. Sustainability 2023, 15, 2386. https://doi.org/10.3390/su15032386
Liu K, Zhao W, Li J, Ding W. Design of Tunnel Initial Support in Silty Clay Stratum Based on the Convergence-Confinement Method. Sustainability. 2023; 15(3):2386. https://doi.org/10.3390/su15032386
Chicago/Turabian StyleLiu, Keqi, Wen Zhao, Jiaxiang Li, and Wantao Ding. 2023. "Design of Tunnel Initial Support in Silty Clay Stratum Based on the Convergence-Confinement Method" Sustainability 15, no. 3: 2386. https://doi.org/10.3390/su15032386
APA StyleLiu, K., Zhao, W., Li, J., & Ding, W. (2023). Design of Tunnel Initial Support in Silty Clay Stratum Based on the Convergence-Confinement Method. Sustainability, 15(3), 2386. https://doi.org/10.3390/su15032386