scholarly journals Limit Analysis of Collapse Mechanisms for Tunnel Roofs Subjected to Pore Water Pressure: A Numerical Approach

2021 ◽  
Vol 2021 ◽  
pp. 1-14
Author(s):  
Jing-jing Liu ◽  
Tie-lin Chen ◽  
Chang-ling Xie ◽  
Jian-hua Tian ◽  
Yu-xin Wei
Keyword(s):  
Pore Water ◽  
Limit Analysis ◽  
Pore Water Pressure ◽  
Water Pressure ◽  
Numerical Approach ◽  
Collapse Mechanism ◽  
Upper Bound Theorem ◽  
Collapse Mechanisms ◽  
Support Force ◽  
Function Expression

The collapse mechanism of a circular unlined tunnel roof subjected to the pore water pressure under plane strain conditions is investigated in this article. First, the model of calculating the function expression of the detaching surface for the collapsing block is formed in the framework of the upper bound theorem of limit analysis and the extremum principle. The analytical solution of the pore water pressure around the tunnel in a two-dimensional steady seepage field is employed in the equations of the model. Then, the numerical approach based on the Runge–Kutta algorithm and traversal search method is proposed to solve the complex equations. The obtained expression of the detaching surface for the collapsing block provides the shape of the collapsing block and a theoretical basis for designing the support force for tunnels. The proposed limit analysis method and numerical approach are verified by comparing with existing theoretical solutions and the numerical simulation result, and they are suitable for deep, shallow tunnels and layered strata. Moreover, the effects of different parameters on the collapse mechanism are investigated, and qualitative results are provided.

Stability assessment of slopes with cracks using limit analysis

2013 ◽  
Vol 50 (10) ◽  
pp. 1011-1021 ◽  
Author(s):  
Radoslaw L. Michalowski
Keyword(s):  
Limit Analysis ◽  
Pore Water Pressure ◽  
Water Pressure ◽  
Crack Depth ◽  
Optimization Procedure ◽  
Collapse Mechanism ◽  
Open Crack ◽  
Stability Assessment ◽  
Critical Height ◽  
Maximum Crack

Cracks are a common occurrence in soil slopes, and a method is described for including the presence of cracks in stability assessment based on the kinematic approach of limit analysis. While many cracks may be present in a slope, the failure mechanism typically involves one crack, whose location has the most adverse influence on stability. A translational mechanism, typical of rock slope failures, is demonstrated to illustrate the method, followed by a rotation collapse analysis that is more appropriate for soils. Pre-existing (open) cracks are considered, as well as the cracks that form as part of the slope collapse mechanism. The maximum crack depth is determined by stability of the vertical crack boundary. This maximum crack depth may be reduced significantly by seepage forces in the slope. The most adverse location of the crack is determined from an optimization procedure where the minimum of the slope critical height is sought. The presence of water is included in the analysis, and stability charts are developed. The influence of the presence of cracks on stability of gentle slopes was not found to be significant, but the effect on the outcome of the analysis increases with an increase in inclination angle and the presence of pore-water pressure. The difference in the critical height of a 60° slope with an open crack and without one can be as much as 50%.

scholarly journals An Analytical Continuous Upper Bound Limit Analysis of Pore Water Effect on the Tail Stability of Underwater Shield Tunnels during Construction

2020 ◽  
Vol 143 ◽  
pp. 01015
Author(s):  
Wenjie Song ◽  
Yanyong Xiang
Keyword(s):  
Pore Water ◽  
Upper Bound ◽  
Limit Analysis ◽  
Pore Water Pressure ◽  
Water Pressure ◽  
Ground Surface ◽  
Support Pressure ◽  
Tunnel Support ◽  
Transverse Stability ◽  
Upper Bound Limit Analysis

An analytical continuous upper bound limit analysis is developed to analyse the effects of seepage on the transverse stability of underwater shield tunnels. The approach is based on an analytical continuous upper bound limit analysis method for cohesive-frictional soils. It employs the complex variables solution of the displacement field due to tunnel deformation and movement, and the analytical solution of the pore water pressure field for steady state seepage due to pore water influx at the tunnel perimeter. The most critical slip line position and the minimum required tunnel support pressure are determined by using a particle swarm optimization scheme for various generic situations. The method is verified via finite element simulation and comparison with the solution from using rigid block upper bound limit analysis. The parametric analysis revealed among other things that both the infimum of the necessary tunnel support pressure and the most critical plastic zone increase when the hydraulic head at the ground surface increases, but decrease when the tunnel influx increases due to the fact that pore water pressure at the tunnel perimeter decreases with the tunnel influx.

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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