Fourth Canadian Geotechnical Colloquium: Strength and slope stability in Canadian soft clay deposits

1981 ◽  
Vol 18 (3) ◽  
pp. 420-442 ◽  
Author(s):  
Guy Lefebvre
Keyword(s):  
Shear Strength ◽  
Slope Stability ◽  
Large Strain ◽  
Soft Clay ◽  
Peak Strength ◽  
Eastern Canada ◽  
Effective Stresses ◽  
Long Term Stability ◽  
Clay Deposits ◽  
Clay Slopes

It is generally admitted that the long term stability of clay slopes should be analysed in terms of effective stresses, which necessitates the knowledge of the pore pressure conditions and of the relationship between the shear strength and the effective stresses. This paper deals with the determination of shear strength for stability analysis of clay slopes in Eastern Canada. First the various concepts pertinent to slope stability in soft clay are examined and a certain justification of the use of the post-peak or large strain strength is demonstrated. In a second part, 14 case records of natural slopes or permanent excavation slopes are presented and analysed in terms of the post-peak strength. Finally, values of post-peak strength determined in the laboratory for more than 30 sites are presented and it is attempted to derive correlations by which the shear strength parameters could be readily approximated from other properties such as the apparent preconsolidation pressure or the vane strength.

Slope instability and valley formation in Canadian soft clay deposits

1986 ◽  
Vol 23 (3) ◽  
pp. 261-270 ◽  
Author(s):  
Guy Lefebvre
Keyword(s):  
Slope Stability ◽  
Soft Clay ◽  
Slope Instability ◽  
Coarse Grained ◽  
Stability Conditions ◽  
Geological Time ◽  
Eastern Canada ◽  
Valley Bottom ◽  
Clay Deposits ◽  
Groundwater Regime

The purposes of the paper are to examine the deepening of valleys in clay deposits of Eastern Canada and in particular to look at the changes in the groundwater regime and slope stability conditions during valley formation. Field observations and laboratory testing indicate that the rate of valley deepening in Champlain clay deposits is of the order of only a few millimetres a year, owing to the low erodibility of the intact clay. The clay banks are, however, more erodible, owing to alteration and fissuration.The stratigraphy of Eastern Canadian clay deposits can be simplified by considering it to be a stratum of low permeabilityconfined between two boundary layers of relatively high permeability, which are the till layer at the base and a weathered crust or coarse-grained layer at the top. As the valley bottom get closer to the bottom till layer, the groundwater regime, and consequently the stability conditions, are modified. During the process of valley formation, the groundwater regime passes through astage where the conditions are rather detrimental to slope stability as it evolves toward conditions that enhance bank stability. Those changes in stability conditions happen over geological time more rapidly or less, depending on clay erodibility. Key words: soft clay, valley formation, slope stability, groundwater, erosion, erodibility.

Stochastic stability analysis of a test excavation involving spatially variable subsoil

2006 ◽  
Vol 43 (10) ◽  
pp. 1074-1087 ◽  
Author(s):  
Yu-Jie Wang ◽  
Paul Chiasson
Keyword(s):  
Shear Strength ◽  
Stability Analysis ◽  
Slope Stability ◽  
Spatial Variability ◽  
Progressive Failure ◽  
Soft Clay ◽  
Stochastic Modelling ◽  
Undrained Shear Strength ◽  
Slope Stability Analysis ◽  
Undrained Shear

A stochastic slope stability analysis method is proposed to investigate the short-term stability of unsupported excavation works in a soft clay deposit having spatially variable properties. Spatial variability of undrained shear strength is modelled by a stochastic model that is the sum of a trend component and a fluctuation component. The undrained shear strength trend, which is also spatially variable, is modelled by kriging or a random function. Slope stability analyses are performed on the stochastic soft clay model to investigate the contribution of spatial variability of undrained shear strength to a disagreement among high factors of safety computed from deterministic methods for slopes that have failed. Probabilities of failure as computed from the stochastic analyses give a better assessment of failure potential. Probability of failure values also correlate with time delay before failure. This phenomenon may be related to progressive failure or creep and to pore pressure dissipation with time.Key words: slope stability analysis, failure probability, spatial variability, stochastic modelling, geostatistics, vane tests, sensitive clay.

scholarly journals Hydrogeology of a complex Champlain Sea deposit (Quebec, Canada): Implications for slope stability

2020 ◽  
Author(s):  
Alexandra Germain ◽  
Nathan Lee Young ◽  
Jean-Michel Lemieux ◽  
A. Locat ◽  
Hugo Delottier ◽  
...  
Keyword(s):  
Slope Stability ◽  
Hydraulic Properties ◽  
Conceptual Models ◽  
Flow System ◽  
Field Site ◽  
Eastern Canada ◽  
Unconfined Aquifers ◽  
Clay Deposits ◽  
Heterogeneous Nature ◽  
Pressure Dynamics

The thick sequences of marine clayey deposits which blanket the St. Lawrence Lowlands in south-eastern Canada are highly susceptible to landslides. With 89% of the population of the Province of Quebec living in this region, improving our understanding of the mechanisms causing landslides in these sediments is a matter of public security. To accomplish this goal, instruments were deployed at a field site in Sainte-Anne-de-la-Pérade, Quebec, Canada to monitor atmospheric, soil, and groundwater conditions. Field and laboratory measurements of soil geotechnical and hydraulic properties were also performed. Results indicate that the groundwater and pore pressure dynamics at the site cannot be explained using simplified site conceptual models. Further analysis indicates that groundwater dynamics and pore pressures in the massive clay deposits on-site are determined by (i) the highly-heterogeneous nature of the local geological materials (ii) the contrasting hydraulic and geotechnical properties of these materials, (iii) the presence of two unconfined aquifers at the site, one surficial and one at depth, and (iv), the presence of the Sainte-Anne River. These results were used to create a new conceptual model which illustrates the complex groundwater flow system present on site, and shows the importance of including hydrogeologic context in slope stability analysis.

Regional geology and landslides in the marine clay deposits of eastern Canada

1970 ◽  
Vol 7 (2) ◽  
pp. 145-156 ◽  
Author(s):  
P. La Rochelle ◽  
J. Y. Chagnon ◽  
G. Lefebvre
Keyword(s):  
Shear Strength ◽  
Pore Water ◽  
Flow Conditions ◽  
Marine Clay ◽  
Eastern Canada ◽  
Regional Geology ◽  
Clay Deposits

A detailed inventory of the numerous landslides which have taken place in the Province of Quebec has shown that they are concentrated in given areas. Extensive studies carried out in three different areas have revealed a coincidence between the concentration of landslides and the existence of valleys in the bedrock underlying the clay deposits.Piezometric levels measured on the field have consistently shown the prevalence of a downward gradient in the upper part of the slope and an upward gradient with artesian pressure at the toe. These flow conditions which can be imputed in part to the presence of the valley in the bedrock produce the leaching of the salt in the pore water of the clay resulting in a decrease of the shear strength and an increase of sensitivity of the clay.

Analysis of Shear Strength Parameters on Soft Clay Slope Stability at Short Term

2012 ◽  
Vol 170-173 ◽  
pp. 1306-1309
Author(s):  
Jing Fang Hou ◽  
Yong Hua Cao ◽  
Shu Wang Yan
Keyword(s):  
Shear Strength ◽  
Slope Stability ◽  
Safety Factor ◽  
Soft Clay ◽  
Strength Parameter ◽  
Statistical Regression ◽  
Shear Strength Parameters ◽  
Strength Parameters ◽  
Short Term ◽  
Clay Ground

The slope stability is an important problem for the slope building on the soft clay ground. At present, the vane shear strength is common used to calculate the factor of slope stability at short term. In fact, a lot of cases show that the vane shear strength underestimates the real shear strength of the sliding surface. Therefore, based on Mohr-Coulomb theory, and using the linear relation between the vane shear strength and the depth, a method of converting in-situ vane shear strength into undrained shear strength parameter is presented. Two shear strength parameters c and φ are from statistical regression analysis. The anisotropy, the lateral compression coefficient and the average consolidation degree of the soft clay are considered. The two shear strength parameters are used to calculate the short term safety factor of the slope stability. The safety factor is greater than 1.0 for steady slope.

Slope Stability Analysis under the Condition of Seepage

2012 ◽  
Vol 204-208 ◽  
pp. 241-245
Author(s):  
Yang Jin
Keyword(s):  
Finite Element Method ◽  
Shear Strength ◽  
Slope Stability ◽  
Negative Impact ◽  
Strength Reduction ◽  
Soil Slope ◽  
Failure State ◽  
Calculation Results ◽  
The Stability ◽  
Shear Strength Reduction

The stability of soil slope under seepage is calculated and analyzed by using finite element method based on the technique of shear strength reduction. When the condition of seepage or not is considered respectively, the critical failure state of slopes and corresponding safety coefficients can be determined by the numerical analysis and calculation. Besides, through analyzing and comparing the calculation results, it shows that seepage has a negative impact on slope stability.

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