scholarly journals Face Stability Analysis of Shield Tunnels in Homogeneous Soil Overlaid by Multilayered Cohesive-Frictional Soils

2016 ◽  
Vol 2016 ◽  
pp. 1-9 ◽  
Author(s):  
Kaihang Han ◽  
Chengping Zhang ◽  
Wei Li ◽  
Caixia Guo
Keyword(s):  
Failure Mechanism ◽  
Shear Failure ◽  
Three Dimensional ◽  
Earth Pressure ◽  
Support Pressure ◽  
Tunnel Face ◽  
Arch Effect ◽  
Theory Approximation ◽  
Homogeneous Soil ◽  
Frictional Soils

In order to better interpret failure features of the failure of soil in front of tunnel face, a new three-dimensional failure mechanism is proposed to analyze the limit support pressure of the tunnel face in multilayered cohesive-frictional soils. The new failure mechanism is composed of two truncated cones that represent the shear failure band and a distributed force acting on the truncated cones that represents the pressure arch effect. By introducing the concept of Terzaghi earth pressure theory, approximation of limit support pressures is calculated using the limit analysis methods. Then the limit support pressures obtained from the new failure mechanism and the existing approaches are compared, which show that the results obtained from the new mechanism in this paper provide relatively satisfactory results.

scholarly journals Rotational Failure Mechanism for Face Stability of Circular Shield Tunnels in Frictional Soils

2019 ◽  
Vol 2019 ◽  
pp. 1-14 ◽  
Author(s):  
Yuan Zhou ◽  
Yuming Zhu ◽  
Shumao Wang ◽  
Hu Wang ◽  
Zhengxing Wang
Keyword(s):  
Failure Mechanism ◽  
Upper Bound ◽  
Pore Water Pressure ◽  
Water Pressure ◽  
Circular Cross Section ◽  
Support Pressure ◽  
Tunnel Face ◽  
Face Stability ◽  
Rotational Failure ◽  
Frictional Soils

Face stability analyses of shield-driven tunnels are often carried out to determine the required support pressure on the tunnel face. Although various three-dimensional mechanisms have been proposed for circular faces of tunnels in frictional and/or cohesive soils to obtain the limit support pressure, the most critical one has not yet been found. Based on a rotational failure mechanism for the frictional soils, this paper modifies the circular cross section as an ellipse to make the generating collapse surface inscribe the entire circular tunnel face. Using the kinematical approach of limit analysis yields an upper bound to the limit support pressure. Through comparisons with the existing results in the literature, the improved mechanism can better estimate the upper bound and is very similar to the observed failures in the experimental tests. The influences of the pore water pressure are also included in the stability analysis of tunnel faces. Calculated upper-bound solutions are presented in a condensed form of charts for convenient use in practice.

scholarly journals Analysis of Instability Mode and Limit Support Pressure of Shallow Tunnel Face in Sands

Symmetry ◽  
2020 ◽  
Vol 12 (12) ◽  
pp. 2067
Author(s):  
Kaihang Han ◽  
Xuetao Wang ◽  
Beibei Hou ◽  
Xingtao Lin ◽  
Chengyong Cao
Keyword(s):  
Stability Analysis ◽  
Shear Failure ◽  
Displacement Sensor ◽  
Support Pressure ◽  
Rapid Decline ◽  
Instability Mode ◽  
High Definition ◽  
Tunnel Face ◽  
Shallow Tunnels ◽  
The Stability

The stability analysis of the tunnel face is not only essential for guaranteeing the safe construction of urban shallow tunnels, but also directly affecting the influence degree of tunnel construction on nearby structures. The primary concerns in the stability analysis of the tunnel face are the instability mode of surrounding rocks and the limit support pressure on the tunnel face. In this paper, face stability of shallow tunnels in sands was conducted using a symmetrical model test. The ground surface settlement, support pressure on the tunnel face and progressive instability modes of sands at tunnel face are measured by using an LVDT (Linear Variable Differential Transformer) displacement sensor, high-precision pressure sensor and high-definition digital camera, respectively. The test results indicate that the shear failure band appears in sands in front of the tunnel face and develops from the tunnel invert to the tunnel crown. The upper sands undergo stress redistribution, and the pressure arch appears with initial form of “ellipsoid”, then of the “pyramid”. Moreover, the support pressure on the tunnel face experiences four stages, namely, rapid decline stage, the minimum stage, slowly raises stage and stable stage during tunnel excavation. The research results of this paper will provide theoretical support for the reasonable value of the support pressure on the tunnel face in practical engineering.

scholarly journals Analysis of the Limit Support Pressure of a Shallow Shield Tunnel in Sandy Soil Considering the Influence of Seepage

Symmetry ◽  
2020 ◽  
Vol 12 (6) ◽  
pp. 1023 ◽  
Author(s):  
Bo Mi ◽  
Yanyong Xiang
Keyword(s):  
Numerical Simulation ◽  
Pore Water ◽  
Pore Water Pressure ◽  
Limit Equilibrium ◽  
Water Pressure ◽  
Three Dimensional ◽  
Support Pressure ◽  
Tunnel Face ◽  
Dimensional Solution ◽  
Physical Model Tests

The objective was to optimize the existing solution for the limit support pressure of a tunnel face. Firstly, based on the numerical simulation results, the existing three-dimensional analytical solution for pore water pressure distribution is expanded to a three-dimensional solution considering the pore water pressure distribution in the upper formation behind the tunnel face. Then, according to the results of physical model tests, a failure model considering the failure range in the upper formation behind the tunnel face is established, and the newly established three-dimensional solution for pore water pressure is introduced into the model, and then the limit effective support pressure of the tunnel face considering seepage is obtained by the method of soil–water joint calculation. Finally, the calculation results in this paper are compared with the experimental results, numerical simulation results and existing theoretical solutions. The major findings are as follows. The distribution of pore water pressure in the front and back strata above the tunnel face is basically symmetrical. The limit effective support pressure of the tunnel face will increase linearly with an increase in the hydraulic head difference between the tunnel face and the ground surface. The calculated results of the new limit equilibrium theory are obviously larger than those of the existing theory and numerical simulation and closer to the results of the physical model tests. Therefore, the new limit equilibrium model can better predict the limit effective support pressure of the tunnel face considering seepage and provide a reference for actual projects.

scholarly journals Probabilistic Analysis of Tunnel Face Stability below River Using Bayesian Framework

2018 ◽  
Vol 2018 ◽  
pp. 1-8 ◽  
Author(s):  
Weiping Liu ◽  
Xiaoyan Luo ◽  
Jinsong Huang ◽  
Lina Hu ◽  
Mingfu Fu
Keyword(s):  
Probabilistic Analysis ◽  
Three Dimensional ◽  
Friction Angle ◽  
Bayesian Framework ◽  
Computational Time ◽  
Support Pressure ◽  
Tunnel Face ◽  
Face Stability ◽  
Mcmc Simulation ◽  
Tunnel Face Stability

A key issue in assessment on tunnel face stability is a reliable evaluation of required support pressure on the tunnel face and its variations during tunnel excavation. In this paper, a Bayesian framework involving Markov Chain Monte Carlo (MCMC) simulation is implemented to estimate the uncertainties of limit support pressure. The probabilistic analysis for the three-dimensional face stability of tunnel below river is presented. The friction angle and cohesion are considered as random variables. The uncertainties of friction angle and cohesion and their effects on tunnel face stability prediction are evaluated using the Bayesian method. The three-dimensional model of tunnel face stability below river is based on the limit equilibrium theory and is adopted for the probabilistic analysis. The results show that the posterior uncertainty bounds of friction angle and cohesion are much narrower than the prior ones, implying that the reduction of uncertainty in cohesion and friction significantly reduces the uncertainty of limit support pressure. The uncertainty encompassed in strength parameters are greatly reduced by the MCMC simulation. By conducting uncertainty analysis, MCMC simulation exhibits powerful capability for improving the reliability and accuracy of computational time and calculations.

scholarly journals Limit Support Pressure of Tunnel Face in Multi-Layer Soils Below River Considering Water Pressure

2018 ◽  
Vol 10 (1) ◽  
pp. 932-939 ◽  
Author(s):  
Weiping Liu ◽  
Lina Hu ◽  
Yongxuan Yang ◽  
Mingfu Fu
Keyword(s):  
Numerical Method ◽  
Limit Equilibrium ◽  
Water Pressure ◽  
Earth Pressure ◽  
Limit Equilibrium Method ◽  
Support Pressure ◽  
Tunnel Face ◽  
Equilibrium Method ◽  
Tunnel Design ◽  
Design And Construction

AbstractThis paper presents a method to determine the limit support pressure of tunnel face in multi-layer soils below river considering the water pressure. The proposed method is based on the 3D Terzaghi earth pressure theory and the wedge theory considering the water pressure. The limit support pressures are investigated using the limit equilibrium method and compared to those calculated using a numerical method, such as FLAC3D. Four cases focusing different combinations of three layers are analyzed. The results obtained by the numerical method agree well with the predictions of the proposed limit equilibrium method. The limit support pressure obtained using the limit equilibrium method is greater than that obtained by the numerical method. The limit equilibrium method is safe and conservative in obtaining the limit support pressure. The proposed limit equilibrium method is expected to be easily adaptable and to enhance the reliability of tunnel design and construction in multi-layer soils below river.

Comparative Analysis of Analytical Method of the Support Pressure at Tunnel Face

2012 ◽  
Vol 256-259 ◽  
pp. 1373-1380
Author(s):  
Chao Li ◽  
Shuai Qi ◽  
Jia Dun Liu
Keyword(s):  
Water Pressure ◽  
Earth Pressure ◽  
Friction Angle ◽  
Support Pressure ◽  
Analytic Method ◽  
Pressure Data ◽  
Tunnel Face ◽  
The Earth ◽  
The Face ◽  
Shield Machine

The shape and properties of the sliding wedge in the three models, DIN4085, Jancsecz and Anagnostou/Kovari, are systematically explained, based on the simple and applied properties by using the analytic method to calculate the earth pressure in the tunnel project with shield machine. Combining with the Silotheory proposed by Janssen and the Terzaghi formula, the three pre-add models are applied to calculate the earth pressure in the projects of the Westerschelde tunnel in Holland, the Metro Line 1 in Düsseldorf and the Mostoles railway in Spain, in comparison with the actual earth pressure data of shield machine. The suitable using conditions of the three models in different situations as the shield type, the buried depth, the soil type, the water pressure and the part of the face are summarized, in which the water pressure, the friction angle and the cohesion of the soil are taking a crucial role in the value of the support pressure.

scholarly journals Study on Stability of Shield Tunnel Excavation Face in Soil-Rock Composite Stratum

2021 ◽  
Vol 2021 ◽  
pp. 1-19
Author(s):  
Hongtao Sui ◽  
Chao Ma ◽  
Chunquan Dai ◽  
Tingzhi Yang
Keyword(s):  
Limit Equilibrium ◽  
Three Dimensional ◽  
Earth Pressure ◽  
Calculation Model ◽  
Shield Tunnel ◽  
Support Pressure ◽  
Finite Element Software ◽  
Dimensional Finite Element ◽  
Practical Engineering ◽  
Three Dimensional Finite Element

In order to study the instability mode of shield excavation face in soil-rock composite stratum and determine the ultimate support pressure of excavation face, this paper selects two typical soil-rock composite strata and uses three-dimensional finite element software to study the failure development process of shield excavation face. Based on the principle of limit equilibrium, a calculation model of limit support pressure for soil-rock composite stratum is proposed and applied to practical engineering. It is found that the shape of “unloading loosening zone” is mainly determined by the properties of upper soil and the properties of lower rock mainly determine the scope and shape of “sliding instability zone.” With the increase of soil proportion coefficient, the ultimate bearing capacity increases nonlinearly and the growth rate decreases gradually. At the same time, the influence of overlying Earth pressure and soil cohesion cannot be ignored.

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