The effect of pore water pressure on tunnel face stability

2016 ◽  
Vol 40 (15) ◽  
pp. 2123-2136 ◽  
Author(s):  
Qiujing Pan ◽  
Daniel Dias
Keyword(s):  
Pore Water ◽  
Pore Water Pressure ◽  
Water Pressure ◽  
Tunnel Face ◽  
Face Stability ◽  
Tunnel Face Stability

In Situ Study on Soil Disturbance Induced by Shield Tunneling in Tianjin

2013 ◽  
Vol 368-370 ◽  
pp. 1674-1677
Author(s):  
Yong Hua Cao ◽  
Xiao Qiang Kou
Keyword(s):  
Pore Water ◽  
Pore Water Pressure ◽  
Water Pressure ◽  
Soil Disturbance ◽  
Ground Settlement ◽  
Soil Pressure ◽  
Shield Tunneling ◽  
Tunnel Face ◽  
Tunneling Process

In urban environment, the soil disturbance induced by shield tunneling can be sensitive because it can cause deformation of the ground and damage the near structure. To study this disturbance in the construction process of Tianjin metro line No.3, in-situ monitoring of pore water pressure, soil pressure and ground settlement were conducted. The pore water pressure was monitored for the soil around the tunnel. The soil pressure was monitored for the soil around the tunnel and on the tunnel face. It was revealed that the pore water pressure and soil pressure changed twice in the tunneling process and these changes were induced by cutting face and grouting at the shield tail. The soil pressure on the tunnel face reached its maximal value when the distance between the cutting face and the sensor elements was around the diameter of the tunnel. Ground settlement developed in the tunneling process. The shape of ultimate settlement trough is closed to the one obtained by Pecks method.

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 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.

Investigation of passive failure and deformation mechanisms due to tunnelling in clay

2013 ◽  
Vol 50 (4) ◽  
pp. 359-372 ◽  
Author(s):  
C.W.W. Ng ◽  
K.S. Wong
Keyword(s):  
Pore Water ◽  
Pore Water Pressure ◽  
Water Pressure ◽  
Diameter Ratio ◽  
Cavity Expansion ◽  
Upper And Lower Bounds ◽  
Tunnel Face ◽  
Excess Pore Water Pressure ◽  
Failure Pressure ◽  
Excess Pore

It is essential to prevent failures at a tunnel face during tunnel construction to protect existing structures and underground utilities. Many studies have investigated active failure in clay, but passive failure is often overlooked. The objectives of this study are to investigate passive failure as well as surface heave and excess pore-water pressure induced by tunnel face displacement in a geotechnical centrifuge. Long-term settlement and dissipation of excess pore-water pressure after passive failure are also investigated. For a tunnel located at a cover to diameter ratio of 2.1, soil in front of the tunnel face is displaced mainly forwards and upwards to the ground surface by the advancing tunnel face. The measured passive failure pressure is closely bounded by the best upper and lower bounds and agrees reasonably well with the cavity expansion solution. For a tunnel located at a cover to diameter ratio of 4.2, a localized failure mechanism is observed. There is a large discrepancy between the measured passive failure pressure and the upper bound solution. Both longitudinal and transverse surface heaves for tunnels located at cover to diameter ratios of 2.1 and 4.2 may be described by two-dimensional Gaussian distributions. The spherical cavity expansion solution appears to overestimate excess pore-water pressure upon passive failure for a tunnel located at a cover to diameter ratio of 2.1. An average of 90% degree of consolidation is reached at time factors of 0.9 and 1.5 for tunnels located at cover to diameter ratios of 2.1 and 4.2, respectively.

TIME TO THE END OF PRIMARY CONSOLIDATION (EOP) OF SOFT CLAYEY SOILS: CONCERNING THE EFFECT OF ATTERBERG’S LIMIT AND CYCLIC LOADING HISTORY

2019 ◽  
Vol 128 (2B) ◽  
pp. 29-41
Author(s):  
Trần Thanh Nhàn
Keyword(s):  
Cyclic Loading ◽  
Pore Water ◽  
Pore Water Pressure ◽  
Water Pressure ◽  
Clayey Soils ◽  
Loading History ◽  
Cyclic Shear ◽  
Wide Range ◽  
Primary Consolidation ◽  
Time Required

In order to observe the end of primary consolidation (EOP) of cohesive soils with and without subjecting to cyclic loading, reconstituted specimens of clayey soils at various Atterberg’s limits were used for oedometer test at different loading increments and undrained cyclic shear test followed by drainage with various cyclic shear directions and a wide range of shear strain amplitudes. The pore water pressure and settlement of the soils were measured with time and the time to EOP was then determined by different methods. It is shown from observed results that the time to EOP determined by 3-t method agrees well with the time required for full dissipation of the pore water pressure and being considerably larger than those determined by Log Time method. These observations were then further evaluated in connection with effects of the Atterberg’s limit and the cyclic loading history.

Conjectures, Hypotheses, and Theories of Drumlin Formation (In memory of Stanislaw Baranowski)

1981 ◽  
Vol 27 (97) ◽  
pp. 503-505 ◽  
Author(s):  
Ian J. Smalley
Keyword(s):  
Shear Strength ◽  
Pore Water ◽  
Stress Level ◽  
Critical Stress ◽  
Pore Water Pressure ◽  
Water Pressure ◽  
Glacial Till ◽  
Forming Process ◽  
Stress Levels

AbstractRecent investigations have shown that various factors may affect the shear strength of glacial till and that these factors may be involved in the drumlin-forming process. The presence of frozen till in the deforming zone, variation in pore-water pressure in the till, and the occurrence of random patches of dense stony-till texture have been considered. The occurrence of dense stony till may relate to the dilatancy hypothesis and can be considered a likely drumlin-forming factor within the region of critical stress levels. The up-glacier stress level now appears to be the more important, and to provide a sharper division between drumlin-forming and non-drumlin-forming conditions.

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