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Stability analysis of tunnel face reinforced with face bolts

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Abstract

Face bolting has been widely utilized to enhance the stability of tunnel face, particularly in soft soil tunnels. However, the influence of bolt reinforcement and its layout on tunnel face stability has not been systematically studied. Based on the theory of linear elastic mechanics, this study delved into the specific mechanisms of bolt reinforcement on the tunnel face in both horizontal and vertical dimensions. It also identified the primary failure types of bolts. Additionally, a design approach for tunnel face bolts that incorporates spatial layout was established using the limit equilibrium method to enhance the conventional wedge-prism model. The proposed model was subsequently validated through various means, and the specific influence of relevant bolt design parameters on tunnel face stability was analyzed. Furthermore, design principles for tunnel face bolts under different geological conditions were presented. The findings indicate that bolt failure can be categorized into three stages: tensile failure, pullout failure, and comprehensive failure. Increasing cohesion, internal friction angle, bolt density, and overlap length can effectively enhance tunnel face stability. Due to significant variations in stratum conditions, tailored design approaches based on specific failure stages are necessary for bolt design.

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Availability of Data/Materials: Dataset generated is available upon reasonable request and within cooperation agreements.

Abbreviations

A :

Cross-section area of the borehole

A dowel :

Cross-section area of the bolt

A t :

Cross-section area of the tunnel

B :

Width of the tunnel

C :

Buried depth of the tunnel

c :

Cohesion force of soil

c collapse :

Limit cohesion at the occur of face collapse

dA :

Lateral area of the soil slice

dF :

Incremental axis force of the bolt

dG :

Gravity of the soil slice

dN :

Normal stress on the sliding surface

dS :

Horizontal resistance

dT :

Tangential stress along the sliding surface

dT fb :

Vertical resistance

dT s :

Shear stress between the soil slice of the reinforced wedge and its adjacent soil mass on both sides of the excavated surface

d s :

Displacement of the sliding wedge on the sliding surface

d h :

Horizontal displacement

d v :

Vertical displacement

d hole :

Diameter of the borehole

d bolt+grout :

Diameter of the bolt and grout

E :

Equivalent Young’s module of the integral of the bolts and grouting

E bolt :

Equivalent Young’s module of the bolts

E grout :

Elastic module of the grout

E soil :

Elastic module of the soil

E s :

Soil reaction modulus

F :

Axis force of the bolt

F w and F ow :

Axial force of bolts embedded within the wedge and outside of the wedge

F test :

Pullout load

H :

Height of the tunnel

I :

Moment of inertia of the bolts

J :

Inertial moment of the bolt section

k :

Foundation coefficient of the soil

L test :

Length of the bolt

l us :

Unsupported span of the tunnel

l w and l ow :

Length of the glass fiber bolt inside the sliding wedge and outside of the wedge

l ol :

Overlap length of the glass fiber bolt

M bolt :

Moment at any point of the bolt

n :

Density of face bolt

n r :

Minimum required face bolt density

P hole :

Area of perimeter of the borehole

P max :

Limit yield pressure of the rock pertaining to localized compression

S dowel :

Static moment of half cross-section of the bolt

T bolt :

Shear force at any point of the bolt

u :

Relative movement between the grouting and soil in the analyzed differential element

u w and u ow :

Movement of bolts embedded within the wedge and outside of the wedge

u test :

Movement of the bolt

V :

Counter-stress exerted by the lower part of the soil slice

w :

Inclination angle of the wedge

z :

Distance from the soil slice to the bottom of the wedge

z 1 :

At which the shear resistance from parts within the wedge and outside the wedge would be the same

z 2 :

When a specific bolt is deployed above this elevation, it would be embedded in the wedge totally and not contribute to the face stability

β :

The inverse of the characteristic length of the bolt

β c :

Shear stiffness at the interface between the grouting and soil

γ :

Unit weight of the soil slice

φ :

Internal friction angle of soil

φ collapse :

Limit frictional angle at the occur of face collapse

λ :

Lateral pressure coefficient

λ w :

Lateral stress ratio for the wedge

τ :

Shear stress at the interface between grouting and soil

τ max :

Maximum value of shear stress at the interface between grouting and soil

τ w and τ ow :

Shear stress of bolts embedded within the wedge and outside of the wedge

ε x :

Strain at the interface between the grouting and soil

σ prism :

Vertical soil pressure

σ x :

Axis stress of the bolt

σ y :

Tensile strength of the bolt

σ z :

Vertical soil stress

ϕ dowel :

Diameter of the bolt

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Acknowledgments

This work is financially supported by the Fundamental Research Funds for the Central Universities, CHD (300102212706), the National Natural Science Foundation of China [Grant No. 52108360], the Science and Technology Project of Department of Transportation of Yunnan Province (No. YJKJ [2019]59).

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Authors and Affiliations

Authors

Contributions

TIAN Chongming, JIANG Yin: methodology, data curation, writing - review and editing. YE Fei, OUYANG Aohui: conceptualization, writing - original draft, validation, investigation. HAN **ngbo: investigation, resources. SONG Guifeng: funding acquisition.

Corresponding authors

Correspondence to Fei Ye or Aohui Ouyang.

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Conflict of Interest: The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

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Tian, C., Jiang, Y., Ye, F. et al. Stability analysis of tunnel face reinforced with face bolts. J. Mt. Sci. 21, 2445–2461 (2024). https://doi.org/10.1007/s11629-023-8400-3

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  • DOI: https://doi.org/10.1007/s11629-023-8400-3

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