Stability Evaluation Model of a Tunnel Face Excavated by the Benching Method in a Soft Silty Clay Layer
Publication: International Journal of Geomechanics
Volume 21, Issue 4
Abstract
With the increasing construction demand for tunnels in soft silty clay layers, it is important to effectively control the face stability of a tunnel. One of the key issues for maintaining face stability is addressing how to accurately obtain the limit support pressure of a tunnel face excavated by the benching method in a soft silty clay layer. Therefore, based on the limit equilibrium method, an improved three-dimensional face stability analysis model is presented in this paper considering the advancing support effect of small pipes. In the model, the sliding failure zone is formed by a log-spiral line. The upper load of the sliding failure zone is shaped by the gravity of the soil, and it can be calculated by a two-parameter elastic foundation beam model when an advanced small pipe is utilized. By comparing these results with the limit support pressure predicted by existing models, the improved model is shown to be reasonable. Finally, the influence of the soil parameters on the limit support pressure is also assessed. The proposed failure mechanism improves the stability analysis of the tunnel face excavated by the benching method in the soft silty clay layer.
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Data Availability Statement
All data, models, and code generated or used during the study appear in the submitted article are available from the corresponding author by request.
Acknowledgments
The authors acknowledge the financial support provided by the National Natural Science Foundation of China (Grant No. 41572275).
Notation
The following symbols are used in this paper:
- A
- base area of the core soil;
- B
- width of the tunnel;
- b
- width of the elastic foundation beam;
- c
- cohesion of soil;
- dz
- thickness of the unit;
- E
- elastic modulus of the advanced small pipe;
- Gp
- shear modulus of the foundation;
- H
- cover depth of the tunnel;
- I
- inertia moment of the advanced small pipe;
- k
- coefficient of the foundation bed;
- la
- distance between logarithmic spiral center and tunnel surface;
- ld
- height of the upper step, which is equal to D/2;
- ls
- length of advanced small pipe;
- Mcy
- moment of the antisliding force;
- Mly
- moment of the support pressure;
- Mqy
- moment of the upper load of the sliding failure zone;
- Mwy
- moment of the soil gravity;
- N
- maximum support force of the core soil on the tunnel face;
- NC
- nondimensional coefficients that represent the effects of cohesion;
- NP
- nondimensional coefficients that represent the effects of surcharge loading;
- Nγ
- nondimensional coefficients that represent the effects of soil weight;
- p(x)
- elastic foundation resistance;
- p0
- upper load above the slide body;
- q(x)
- surrounding rock pressure;
- q0
- equivalent uniform load above the slide body;
- r
- vectorial diameter of the logarithmic spiral;
- r0
- length of the logarithmic spiral when polar angle is zero;
- S1
- moment of the support pressure in area S1;
- S2
- moment of the support pressure in area S2;
- W
- gravity of the core soil;
- γ
- soil gravity;
- θ
- polar angle of the logarithmic spiral;
- λ
- lateral pressure coefficient;
- ρ
- horizontal length of the slip microelement;
- σT
- limit support pressure of the core soil on the tunnel face;
- limit support pressure of area ECHG;
- φ
- friction angle of soil;
- ω
- rotation angle of the unit; and
- ω(x)
- deflection of the advanced small pipe.
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Published In
International Journal of Geomechanics
Volume 21 • Issue 4 • April 2021
Copyright
© 2021 American Society of Civil Engineers.
History
Received: May 13, 2020
Accepted: Oct 29, 2020
Published online: Jan 29, 2021
Published in print: Apr 1, 2021
Discussion open until: Jun 29, 2021
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