Embankment failures at Vernon, British Columbia

1995 ◽  
Vol 32 (2) ◽  
pp. 271-284 ◽  
Author(s):  
C.B. Crawford ◽  
R.J. Fannin ◽  
C.B. Kern
Keyword(s):  
Case History ◽  
Field Observation ◽  
Factor Of Safety ◽  
Strain Softening ◽  
Progressive Failure ◽  
Back Analysis ◽  
Site Investigation ◽  
Silty Clay ◽  
Pore Pressures ◽  
Similar Materials

A section of Highway 97, west of Vernon, B.C., is located over a soft-to-firm, compressible, silty clay subsoil. In addition to an extensive site investigation, the performance of two test embankments was observed for 2 years before construction was begun on the highway grade between them. When the highway fill reached a maximum thickness of about 10 m a failure occurred. The design was then changed to include berms on either side, but a second failure occurred when the grade was rebuilt. An undrained back-analysis of the first failure shows the influence of various variables on the factor of safety and illustrates the difficulty of choosing appropriate strength values for design when the site has a strong crust overlying a weaker layer and there is potential for progressive failure. Observations of settlements, pore pressures, and lateral movements in the subsoil describe the performance of the embankment during construction and reveal the importance of strain softening as a factor in the failures. Comparisons with a variety of similar failures in Canada, Scandinavia, and southeast Asia provide some guidance for future construction over similar materials. Key words : case history, embankment failure, field observation, pore pressures, stability, strength, undrained analysis.

Progressive failure of the Carsington Dam: a numerical study

1992 ◽  
Vol 29 (6) ◽  
pp. 971-988 ◽  
Author(s):  
Z. Chen ◽  
N. R. Morgenstern ◽  
D. H. Chan
Keyword(s):  
Finite Element Analysis ◽  
Finite Element ◽  
Factor Of Safety ◽  
Progressive Failure ◽  
Limit Equilibrium ◽  
Equilibrium Analysis ◽  
Element Analysis ◽  
Limit Equilibrium Analysis ◽  
The Finite Element Analysis ◽  
Yellow Clay

The mechanism of progressive failure is well understood as one which involves nonuniform straining of a strain-weakening material. Traditional limit equilibrium analysis cannot be used alone to obtain a rational solution for progressive failure problems because the deformation of the structure must be taken into account in the analysis. The failure of the Carsington Dam during construction in 1984 has been attributed to progressive failure of the underlying yellow clay and the dam core materials. The dam was monitored extensively prior to failure, and an elaborate geotechnical investigation was undertaken after failure. The limit equilibrium analysis indicated that the factors of safety were over 1.4 using peak strength of intact clay material or 1.2 based on reduced strength accounting for preshearing of the yellow clay layer. Factors of safety were found to be less than unity if residual strengths were used. The actual factor of safety at failure was, of course, equal to one. By using the finite element analysis with strain-weakening models, the extent and degree of weakening along the potential slip surface were calculated. The calculated shear strength was then used in the limit equilibrium analysis, and the factor of safety was found to be 1.05, which is very close to the actual value of 1.0. More importantly, the mechanism of failure and the initiation and propagation of the shear zones were captured in the finite element analysis. It was also found that accounting explicitly for pore-water pressure effects using the effective stress approach in the finite element and limit equilibrium analyses provides more realistic simulations of the failure process of the structure than analyses based on total stresses. Key words : progressive failure, strain softening, finite element analysis, dams.

Back Analysis for Mass Parameters of Tunnel Surrounding Rock

2012 ◽  
Vol 170-173 ◽  
pp. 20-24 ◽  
Author(s):  
Kai Cui ◽  
Xue Kai Pan
Keyword(s):  
Deformation Mechanism ◽  
Strain Softening ◽  
Back Analysis ◽  
Surrounding Rock ◽  
Tunnel Engineering ◽  
Railway Tunnel ◽  
Displacement Back Analysis ◽  
Information Construction ◽  
Engineering Information ◽  
The Common

Tunnel engineering information construction has been widely used, and the back analysis is its core. As the common useful method, displacement back analysis is of special advantages. This paper introduces the calculative method based on the application in a railway tunnel. The result shows that strain softening model can be used to simulate the large deformation mechanism of surrounding rock.

scholarly journals Factor of Safety Reduction Factors for Accounting for Progressive Failure for Earthen Levees with Underlying Thin Layers of Sensitive Soils

2013 ◽  
Vol 2013 ◽  
pp. 1-13 ◽  
Author(s):  
Adam J. Lobbestael ◽  
Adda Athanasopoulos-Zekkos ◽  
Josh Colley
Keyword(s):  
Finite Element ◽  
Strain Softening ◽  
Progressive Failure ◽  
Limit Equilibrium ◽  
Thin Layers ◽  
The Finite Element Method ◽  
Element Analysis ◽  
Limit Equilibrium Methods ◽  
The Stability ◽  
Reduction Factors

The effects of progressive failure on flood embankments with underlying thin layers of soft, sensitive soils are investigated. Finite element analysis allows for investigation of strain-softening effects and progressive failure in soft and sensitive soils. However, limit equilibrium methods for slope stability analysis, widely used in industry, cannot capture these effects and may result in unconservative factors of safety. A parametric analysis was conducted to investigate the effect of thin layers of soft sensitive soils on the stability of flood embankments. A flood embankment was modeled using both the limit equilibrium method and the finite element method. The foundation profile was altered to determine the extent to which varying soft and sensitive soils affected the stability of the embankment, with respect to progressive failure. The results from the two methods were compared to determine reduction factors that can be applied towards factors of safety computed using limit equilibrium methods, in order to capture progressive failure.

Soft zones in the glacial till in downtown Edmonton

1982 ◽  
Vol 19 (2) ◽  
pp. 175-180 ◽  
Author(s):  
S. Thomson ◽  
R. L. Martin ◽  
Z. Eisenstein
Keyword(s):  
Recent Work ◽  
Case History ◽  
Early Experience ◽  
Site Investigation ◽  
Glacial Till ◽  
Geological Model ◽  
High Rise ◽  
Material Type ◽  
Spread Footings

High-rise buildings in downtown Edmonton have generally been founded on spread footings in glacial till. Early geotechnical work proposed a geological model comprising uniform, very dense basal (lodgement) till. However, recent work shows that the till is more complex, being variable in both material type and consistency. A case history is described that exemplifies this variability. It is concluded that early experience with the dense tills has led to an overconfident approach to soil investigation in this area and that a thorough site investigation is required.

Progressive failures in eastern Canadian and Scandinavian sensitive clays

2011 ◽  
Vol 48 (11) ◽  
pp. 1696-1712 ◽  
Author(s):  
Ariane Locat ◽  
Serge Leroueil ◽  
Stig Bernander ◽  
Denis Demers ◽  
Hans Petter Jostad ◽  
...  
Keyword(s):  
Failure Mechanism ◽  
Strain Softening ◽  
Progressive Failure ◽  
Earth Pressure ◽  
Failure Surface ◽  
Eastern Canada ◽  
Stress Strain ◽  
Softening Behaviour ◽  
Strain Behaviour

Observations from past events are used to show that the concept of progressive failure may explain translational progressive landslides and spreads — large landslides occurring in sensitive clays. During progressive failure, the strain-softening behaviour of the soil causes unstable forces to propagate a failure surface further in the slope. Translational progressive landslides generally take place in long, gently inclined slopes. Instability in a steeper upslope area is followed by redistribution of stress, which increases earth pressure further downslope. Passive failure may therefore occur in less-inclined ground, heaving the soil. Spreads are usually trigged by erosion of a deposit having a higher angle near the toe. Instability starts near the toe of the slope and propagates into the deposit, reducing earth pressure. This may lead to the formation of an active failure with dislocation of the deposit into horsts and grabens. The failure mechanism of both types of landslides is controlled by the stresses in the slope and the stress–strain behaviour of the soil. The mechanism presented explains the sensitivity of a slope to minor disturbances and the resulting high retrogressions observed for such landslides in Scandinavia and eastern Canada.

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