scholarly journals 3D Numerical Investigation of Face Stability in Tunnels with Unsupported Face

2021 ◽  
Author(s):  
DIMITRIOS GEORGIOU ◽  
ALEXANDROS KALOS ◽  
MICHAEL KAVVADAS
Keyword(s):  
Stability Parameter ◽  
Volume Loss ◽  
Tunnel Wall ◽  
Tunnel Face ◽  
Face Stability ◽  
Ground Conditions ◽  
The Face ◽  
Suitable Combination ◽  
Average Face ◽  
The Stability

Abstract The paper studies the stability of unsupported tunnel faces by analyzing the results of a large number of 3D numerical analyses of tunnel faces, in various ground conditions and overburden depths. The analyses calculate the average face extrusion (Uh) by averaging the axial displacement over the tunnel face. Limiting face stability occurs when the average face extrusion becomes very large and algorithmic convergence becomes problematic. Using the results of the analyses, a dimensionless “face stability parameter” is defined, which depends on a suitable combination of ground strength, overburden depth and tunnel width. The face stability parameter correlates very well with many critical tunnel face parameters, like the safety factor of the tunnel against face instability, the average face extrusion, the radial convergence of the tunnel wall at the excavation face, the volume loss and the deconfinement ratio at the tunnel face. Thus, semi-empirical formulae are proposed for the calculation of these parameters in terms of the face stability parameter. Since the face stability parameter can be easily calculated from basic tunnel and ground parameters, the above critical tunnel parameters can be calculated, and conclusions can be drawn about tunnel face stability, volume loss and the deconfinement ratio at the excavation face which can be useful in preliminary tunnel designs.

Three-Dimensional Analysis of Excavating Face Stability Supported by Pipe Roof

2013 ◽  
Vol 275-277 ◽  
pp. 1257-1263 ◽  
Author(s):  
Xiang Yuan ◽  
Shun Hua Zhou ◽  
Quan Mei Gong
Keyword(s):  
Analytical Solution ◽  
Dimensional Analysis ◽  
Load Transfer ◽  
Three Dimensional ◽  
Subgrade Reaction ◽  
Large Section ◽  
Tunnel Face ◽  
Face Stability ◽  
Tunnel Face Stability ◽  
The Stability

This paper analyzes the load transfer characteristics of pipe roof over the excavating face, and the analytical solution of tunnel face stability is established by the method of three-dimensional analysis. Through the calculation of the load transfer of the pipe roof, it indicates that the released load of excavation is passed to the supporting structure and soil which is not excavated by the effect of the pipe roof, and the magnitude of load and coverage of impact are in connection with excavating footage as well as subgrade reaction. The three-dimensional analytical solution of tunnel face stability is used to analyze a project case of Airport Road underpass in Hangzhou. The results show that the tunnel face stability is not guaranteed when excavated on a large section while the stability is enhanced when excavated on separated pilot headings.

scholarly journals Upper Bound Solution for the Face Stability of Shield Tunnel below the Water Table

2014 ◽  
Vol 2014 ◽  
pp. 1-11 ◽  
Author(s):  
Xilin Lu ◽  
Haoran Wang ◽  
Maosong Huang
Keyword(s):  
Upper Bound ◽  
Limit Analysis ◽  
Fe Simulation ◽  
Shield Tunnel ◽  
Support Pressure ◽  
Seepage Force ◽  
Tunnel Face ◽  
Face Stability ◽  
The Face ◽  
Upper Bound Limit Analysis

By FE simulation with Mohr-Coulomb perfect elastoplasticity model, the relationship between the support pressure and displacement of the shield tunnel face was obtained. According to the plastic strain distribution at collapse state, an appropriate failure mechanism was proposed for upper bound limit analysis, and the formula to calculate the limit support pressure was deduced. The limit support pressure was rearranged to be the summation of soil cohesionc, surcharge loadq, and soil gravityγmultiplied by their corresponding coefficientsNc,Nq, andNγ, and parametric studies were carried out on these coefficients. In order to consider the influence of seepage on the face stability, the pore water pressure distribution and the seepage force on the tunnel face were obtained by FE simulation. After adding the power of seepage force into the equation of the upper bound limit analysis, the total limit support pressure for stabilizing the tunnel face under seepage condition was obtained. The total limit support pressure was shown to increase almost linearly with the water table.

Influence of Pipe Roof Reinforcement on Face Stability of Underwater Tunnel

2011 ◽  
Vol 261-263 ◽  
pp. 1029-1033 ◽  
Author(s):  
Kai Wang ◽  
Hai Gui Kang ◽  
Hai Tao Wang
Keyword(s):  
Support Pressure ◽  
Seepage Force ◽  
Tunnel Face ◽  
Face Stability ◽  
Seepage Pressure ◽  
Kinematic Method ◽  
The Face ◽  
Tunnel Face Stability ◽  
Underwater Tunnel ◽  
Groundwater Flow Condition

The effect of seepage force on tunnel face stability with pipe roof reinforcement was studied based on the kinematic method of limit analysis. This method can be employed to define the safety factor and its corresponding critical failure mechanism for a given tunnel. The studies revealed that the existence of groundwater may seriously affect the face stability. Under the steady-state groundwater flow condition, most part of the total support pressure is owing to the seepage pressure acting on the tunnel face. There was a relatively large reduction in the seepage pressure by adopting the pipe roof reinforcement technique.

Test Study on the Influence of Interface of Soil and Rock on the Stability of Sandy Soil Tunnel Face

2012 ◽  
Vol 226-228 ◽  
pp. 1509-1512
Author(s):  
Jian Jun Tong ◽  
Ming Nian Wang ◽  
Hu Jin
Keyword(s):  
Sandy Soil ◽  
Failure Surface ◽  
Model Tests ◽  
Surface Shape ◽  
Tunnel Face ◽  
Test Study ◽  
The Face ◽  
The Stability

Through model tests, three different locations of the interface of the soil and rock in sandy soil tunnel were simulated. The failure processes of the face and the un-supported section were described. The initial and finial depth-width ratios were obtained. The failure features and mechanism were analyzed. The tests show that the longitudinal equilibrium arch in the un-supported section fist forms, and then the tunnel face damages. The failure surface shape approximates to logarithm spire curve, and it is the interface of the soil and rock when there is the interface of the soil and rock in front of the tunnel face. The interface of the soil and rock improves the stability and the depth-width ratios of the tunnel face and the un-supported section, especially when it is in front of the tunnel face.

Failure modes and face instability of shallow tunnels under soft grounds

2018 ◽  
Vol 28 (4) ◽  
pp. 566-589 ◽  
Author(s):  
Zhiqiang Zhang ◽  
Huayun Li ◽  
Hongyu Yang ◽  
Bo Wang
Keyword(s):  
Failure Modes ◽  
Pressure Coefficient ◽  
Soil Formation ◽  
Sandy Soils ◽  
Theoretical Models ◽  
Upper Bound Theorem ◽  
Tunnel Face ◽  
Face Stability ◽  
Shallow Tunnels ◽  
The Face

For shallow tunnels under soft grounds, it is very difficult to gain a complete understanding on all the load-bearing arch effects during excavation, since such tunnels can easily deform or even collapse. Among these effects, the tunnel face stability plays the most important role and has not been understood and handled very well; therefore, the design and construction of such tunnels under soft grounds remain as a challenge. In this work, the different failure models of face instability of the shallow tunnels were established based on the upper-bound theorem of limit analysis for the formation of clayey and sandy soils, respectively, and the analytical equations for determining the limit support force for the face stability were also derived. Furthermore, the influences of various factors on the stability were analyzed and compared. For the sandy soil formation, an equivalent pressure coefficient was proposed for the tunnel faces of bolt reinforcement. Finally, taking the face stability of the shallow tunnels in sandy soils as an example, a complete numerical simulation was conducted to verify the accuracy and effectiveness of the analytical results based on the theoretical models as well as their application conditions.

scholarly journals Face Stability Analysis of Shield Tunnel Using Slip Line Method

2019 ◽  
Vol 2019 ◽  
pp. 1-9
Author(s):  
Weiping Liu ◽  
Shaofeng Wan ◽  
Xinqiang Song ◽  
Mingfu Fu ◽  
Lina Hu
Keyword(s):  
Stability Analysis ◽  
Slip Line ◽  
Yield Criterion ◽  
Limit Equilibrium ◽  
Shield Tunnel ◽  
Support Pressure ◽  
Tunnel Face ◽  
Face Stability ◽  
Line Method ◽  
The Stability

The sufficient support pressure is essential to guarantee the safe construction of shield tunnel. Thus, it is necessary to analyze the stability and assess the limit support pressure of the tunnel face. The main methods for face stability analysis mostly focused on finite element method, limit equilibrium method, and numerical simulation method. In this paper, the slip line method is applied to analyze the stability of the tunnel face. The soil is supposed as ideal isotropic, homogeneous, and incompressible continuous material, which obeys the Mohr–Coulomb yield criterion. A mathematical model of the limit equilibrium boundary value problem is established. The slip line method is used to solve the slip line field and stress field of the soil behind the tunnel face. Limit support pressure and failure mechanism of the tunnel face are then obtained. In addition, comparisons between the results of this study and those of existing approach are performed, and the influence factors are also discussed. The results show that the slip line method is proven to be reliable for the evaluation of limit support pressure of the tunnel face stability.

Probabilistic analysis of tunnel face stability considering spatially variable undrained shear strength with linearly increasing mean trend

2020 ◽  
pp. 1748006X2092715
Author(s):  
Hongzhan Cheng
Keyword(s):  
Shear Strength ◽  
Finite Difference ◽  
Finite Difference Method ◽  
Difference Method ◽  
Undrained Shear Strength ◽  
Tunnel Face ◽  
Face Stability ◽  
Tunnel Face Stability ◽  
The Stability ◽  
Undrained Shear

The inherent spatial variability of soil properties has been considered as one of the main sources of uncertainties in geotechnical problems. The need for probabilistic analysis of the tunnel face stability that takes into account the variability of soil properties has been acknowledged. This article employed a probabilistic-based method, called random finite difference method, for evaluating the stability of tunnel face under the influence of the variability of undrained shear strength in clays. The two-dimensional spatial variation in soil undrained shear strength is modeled by random fields, which are discretized by the Covariance Matrix Decomposition method. The procedure for random finite difference method is presented. An illustrative example is employed to investigate the effect of soil variability. Particular attention has been paid to the situation that undrained shear strength increases with depth. The results demonstrate that ignoring the variability of undrained shear strength will result in overestimates of the tunnel face stability if the support pressure of the tunnel face exceeds the deterministic value, especially for higher coefficient of variation of soil undrained shear strength. Minor differences in the failure mechanism are observed in comparison to the deterministic case, considering only the global failure of the tunnel face is observed. In addition, ignoring the increase of undrained shear strength with depth will lead to conservative designs. The random finite difference method can provide a practical tool for evaluating the stability of a tunnel face in variable soils.

scholarly journals Analisis Stabilitas dan Deformasi Terowongan Kereta Cepat Indonesia dengan Pendekatan Numerik Tiga Dimensi

2021 ◽  
Vol 6 (2) ◽  
pp. 111
Author(s):  
Rinaldi Alamsyah ◽  
Indra Noer Hamdhan
Keyword(s):  
Static Analysis ◽  
Safety Factor ◽  
Tunnel Face ◽  
Face Stability ◽  
Level Of Activity ◽  
Tunnel Face Stability ◽  
The Stability ◽  
High Level ◽  
Double Track ◽  
Plaxis 3D

ABSTRAKWilayah perkotaan yang didalamnya terdapat perkantoran dan tempat yang memiliki tingkat kegiatan yang sangat tinggi, menjadikan struktur terowongan bawah tanah sebagai salah satu solusi untuk meningkatkan infrastruktur transportasi secara  optimal. Terowongan kereta cepat Indonesia merupakan salah satu terowongan yang dibangun dan berlokasi di Halim, DKI Jakarta. Terowongan dengan panjang 1.885 m ini memiliki jalur ganda (Double Track Railway). Untuk mengetahui stabilitas dan deformasi terowongan pada saat konstuksi, dilakukan analisis geoteknik. Analisis yang dilakukan yaitu analisis statik dan kondisi longterm dengan analisis dinamik. Tunneling Bore Machine (TBM) dengan sistem perkuatan linning precast dan grouting dipilih sebagai metode konstruksi untuk membangun terowongan. Pemodelan analisis statik menghasilkan deformasi terbesar 0,03056 m dan nilai faktor keamanan 1,869.Kata kunci: terowongan kereta cepat Indonesia, stabilitas, deformasi, faktor keamanan, TBM, PLAXIS 3D, linning, grouting ABSTRACTUrban areas with offices and places that have a very high level of activity make underground tunnel structures one of the solutions to optimally improve transportation infrastructure. The Indonesian fast train tunnel is one of the tunnels built and located at Halim, DKI Jakarta. The tunnel with a length of 1,885 m has a double track (Double Track Railway). To determine the stability and deformation of the tunnel during construction, a geotechnical analysis was performed. The analysis performed is static analysis and longterm conditions with dynamic analysis. Tunneling Bore Machine (TBM) with precast linning reinforcement and grouting system was chosen as the construction method for tunneling. Static analysis modeling produces the largest deformation 0.03056 m and a safety factor value of 1.869.Keywords: tunnel, face stability, deformation, safety factor, TBM, numerical method, PLAXIS 3D, linning, grouting

Site Experiment for Predicting Hazardous Geological Formations ahead of Tunnel Face

2006 ◽  
Vol 326-328 ◽  
pp. 461-464 ◽  
Author(s):  
C.N. Lin ◽  
Yu Yong Jiao ◽  
Q.S. Liu
Keyword(s):  
Spatial Information ◽  
Test Procedure ◽  
Railway Tunnel ◽  
Tunnel Face ◽  
Drilling Method ◽  
The Face ◽  
The Stability ◽  
The Moment ◽  
Under Construction ◽  
Short Time

In the construction of railways in western part of China, more and more long tunnels have been excavated these years, and several ones are under construction at the moment. Because of the complex geologies like faults, fractured zones, karst cavities as well as water bearing formations, the stability and safety of tunnels have been challenging topics in the construction process. In this regard, the advance knowledge of the location, size, and spatial information of the uncertainties ahead of the face is very important to the contractors. In this paper, by using the Tunneling Seismic Prediction (TSP) technique, site experiments are performed to predict hazardous formations ahead of face in a railway tunnel. Through interpretation of the testing data, the wave velocities and the mechanical parameters of the surrounding rock are obtained, and the faults/fractures are recognized. The study shows that compared to time-consuming core drilling method, the wave reflection based TSP method can predict major uncertain formations in long range ahead of the face in short time. The downtime, as we know, is one of the key factors in speeding the tunnel construction. For the prediction accuracy, the TSP technique is able to provide enough information due to its multiple proof-test procedure.

scholarly journals Analysis of Face Stability of Circular Tunnel in Purely Cohesive Soils Driven by Shield

2018 ◽  
Author(s):  
Jinhui Liu ◽  
Wantao Ding ◽  
Mingbin Wang
Keyword(s):  
Analytical Model ◽  
Yield Criterion ◽  
Failure Process ◽  
Support Pressure ◽  
Cohesive Soils ◽  
Soil Arching ◽  
Circular Tunnel ◽  
Tunnel Face ◽  
Face Stability ◽  
The Face

Based on the kinematic approach of the limit analysis and slip-line theories, this paper proposes a new 2D analytical model to evaluate the collapse support pressure to ensure the face stability of a circular tunnel in purely cohesive soils driven by a shield. The normality conditions, the yield criterion and the vertical soil arching effect are considered in the analytical model. Two upper bound solutions corresponding to the ratio of the cover to the diameter (C/D) are derived from considering the mechanisms based on the motion of rigid multi-blocks. Comparisons are made with existing upper and lower bound solutions published in previous articles. The results are close to the solutions of practical engineering. The failure mechanisms proposed in this study provide a better explanation for the failure process in the heading of the tunnel face.

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