Coupled FDM–DEM Method for Analyzing EPBS Machine Tunneling Performance in Boulders
Publication: International Journal of Geomechanics
Volume 22, Issue 12
Abstract
This work focuses on the development of a three-dimensional shield tunneling model coupling the finite-difference method (FDM) with the discrete-element method (DEM) and evaluates its tunneling performance in boulders. The tunneling process of cutterhead rotation, cutting the formation, soil entering the chamber, and discharging of the screw conveyor is simulated to explain the characteristics of particle movement in front of the tunnel face. The range of the soil failure zone under different shield discharge ratios is determined by the correlation between the discharge ratio and the tunnel surface stability. The evolution process of the soil arching effect in the boulders along with shield tunneling is investigated to understand the mechanisms of the delay settlement in the boulders. Subsequently, the shield discharge ratio is optimized by investigating its influence on the surface deformation. Finally, the average stress distribution on the shield cutterhead in the tunneling process is analyzed to provide the scheme of the cutterhead structure and arrangement. This work can be referred for evaluating the shield tunneling performance and optimizing the excavation design scheme of shield machines during tunneling construction under similar geological conditions.
Practical Applications
The coupled finite-difference method (FDM)–discrete-element method (DEM) calculation method proposed in this study was successfully applied for boring tunnel equipment performance analysis in Beijing Metro Line 16. This shield tunnel was excavated in the strata with boulders rich in large size and high strength, and the previous tunneling experience shows that the shield is prone to encountering accidents such as tool damage and cutterhead jamming by large boulders when tunneling in such strata. Based on the present parametric analysis and calculation results, the suitable engineering suggestions have been proposed to enhance the shield equipment specifically, such as strengthening the central and peripheral cutters and the wear resistance of the cutterhead sides. In addition, the cutterhead opening and band-type screw conveyor were also adjusted to allow large size stones to pass through the cutterhead and discharge from the soil chamber as much as possible instead of being broken by the cutters. The adoption of these techniques has made it possible for the earth pressure balance shield (EPBS) machine to continuously excavate 1,300 m in boulders without cutter exchanges.
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Acknowledgments
This study was financially supported by the National Natural Science Foundation of China (Grant No. U1261212). The authors would like to acknowledge the China Railway Electrification Bureau Group for providing engineering data. In addition, the authors thank the first author’s senior alumni, Dr. Jinguo Cheng, for his suggestions in writing and revision.
Notation
The following symbols are used in this paper:
- Ai
- area of facet i;
- c
- cohesion;
- cu
- soil undrained shear strength;
- D
- outer diameter of the tunnel;
- d
- particle diameter;
- E
- elastic modulus;
- force vector of facet i;
- Fc,N
- projection of in the normal direction of facet i;
- fs
- supporting pressure on the tunnel face;
- H
- thickness of the overlying soil of the tunnel;
- h
- thickness of the soil layer;
- K
- measurement factor;
- K
- stiffness ratio;
- l
- tunneling distance;
- M
- cumulative amount of belt conveyors discharge;
- N
- stability factor of the tunnel face;
- NTC
- collapse stability factor of the tunnel face;
- P0, P1, P2
- coordinate points of the vertex of facet i;
- Qc
- belt load;
- Qin
- volume of soil entering the chamber;
- Qin,th
- theoretical volume of the muck entering the soil chamber;
- Qout
- volume of soil discharged from the chamber;
- R
- discharge ratio;
- normal vector of facet i;
- Smax
- maximum subsidence on ground surface;
- Vc
- belt speed;
- VL,f
- volume loss in tunnel excavation;
- α
- soil looseness coefficient;
- γ
- soil unit weight;
- γsat
- soil saturated unit weight;
- μ
- friction coefficient;
- ν
- Poisson’s ratio;
- ϕ
- friction angle;
- σ0
- earth pressure at the depth of the tunnel centerline;
- σf,i
- stress for facet i; and
- φ
- internal friction angle.
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Information & Authors
Information
Published In
International Journal of Geomechanics
Volume 22 • Issue 12 • December 2022
Copyright
© 2022 American Society of Civil Engineers.
History
Received: Feb 23, 2022
Accepted: Jun 30, 2022
Published online: Oct 11, 2022
Published in print: Dec 1, 2022
Discussion open until: Mar 11, 2023
ASCE Technical Topics:
- Boulders
- Construction equipment
- Coupling
- Discrete element method
- Engineering fundamentals
- Equipment and machinery
- Geology
- Geomechanics
- Geotechnical engineering
- Methodology (by type)
- Models (by type)
- Numerical methods
- Rocks
- Soil dynamics
- Soil mechanics
- Soil settlement
- Structural engineering
- Structural members
- Structural systems
- Three-dimensional models
- Tunneling
- Tunnels
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