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.

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.

Groundwater regime associated with slope stability in Champlain clay deposits

1980 ◽  
Vol 17 (1) ◽  
pp. 44-53 ◽  
Author(s):  
Jean Lafleur ◽  
Guy Lefebvre
Keyword(s):  
Finite Element Method ◽  
Finite Element ◽  
Slope Stability ◽  
Aquifer Recharge ◽  
The Finite Element Method ◽  
Stability Of Slopes ◽  
Clay Deposits ◽  
Groundwater Regime ◽  
The Stability ◽  
Element Method

Slope stability analyses in terms of effective stresses are most often based on hypothetical conditions of pore pressure. It is generally assumed that the flow occurs parallel to the slope or even that the conditions are hydrostatic. In fact, in situ measurements tend to show that the real situation could significantly deviate from these approximations due to geologic conditions. The influence of various geometric and stratigraphic factors on the groundwater regime and on the stability of slopes was studied with the finite-element method. To illustrate the parametric study, experimental evaluations of the flow patterns are presented at four sites. The stratigraphy and permeability measurements combined with the finite-element method enabled a complete flow net to be drawn and although some hypotheses had to be formulated with regards to the underlying aquifer recharge or permeability anisotropy, reasonable agreement was found between simulated and measured piezometric heads.

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.

scholarly journals The contribution of chestnut coppice forests on slope stability in abandoned territory: a case study

2013 ◽  
Vol 44 (2s) ◽  
Author(s):  
Chiara Bassanelli ◽  
Gian Battista Bischetti ◽  
Enrico Antonio Chiaradia ◽  
Lorenzo Rossi ◽  
Chiara Vergani
Keyword(s):  
Slope Stability ◽  
Root Diameter ◽  
Slope Instability ◽  
Economic Changes ◽  
Sweet Chestnut ◽  
Forestry Practices ◽  
Short Rotation ◽  
Root Cohesion ◽  
Chestnut Coppice ◽  
High Level

Sweet chestnut has been for many centuries fundamental for the Italian mountainous economies, where this kind of forest was traditionally managed in short rotation to rapidly produce wood biomass. Due to the social and economic changes, which made such management scheme unprofitable especially on the steep and remote slopes, such practice has been mainly abandoned and most of chestnut forests became over-aged and very dense, causing an increase of localized slope instability. In this work the effect of over-aged chestnut coppice forests on shallow landslides was analysed by evaluating and comparing mechanical contribution to soil shear strength provided by root systems in differently managed chestnut stands. The study area is located in Valcuvia (Lombardy Prealps) where three different stands, one managed and the others abandoned (over 40 year aged), established on cohesionless slopes (quaternary moraine deposits) were chosen having care to select homogeneous conditions in terms of substrate, aspect and elevation. As slope steepness strongly affects forestry practices and steeper stands are more frequently abandoned, the considered stands have different terrain inclination, 30-35° in abandoned stands and 13° in the managed one. Slope stability of the three sites was evaluated by applying the infinite slope approach accounting for additional root cohesion and tree surcharge. Additional root cohesion was estimated through the Fiber Boundle Model approach by collecting roots in the field and measuring their resistance in laboratory, and by measuring root diameter and density distribution with depth by the wall technique method. The results, as expected, showed that over-aging does not affect root mechanical properties, whereas it significantly affects root distribution within the soil. In terms of slope stability, when steepness exceeds 35°, instability phenomena can be triggered by high level of soil saturation in the case of over-aged forests, whereas for less extreme cases chestnut forests, although over-aged, are able and fundamental to guarantee safe conditions.

scholarly journals Probability Assessment of Slope Instability in Seasonally Cold Regions under Climate Change

2021 ◽  
Author(s):  
Yulong Zhu ◽  
Tatsuya Ishikawa ◽  
Tomohito J. Yamada ◽  
Srikrishnan Siva Subramanian
Keyword(s):  
Climate Change ◽  
Slope Stability ◽  
Water Content ◽  
Air Temperature ◽  
Climate Changes ◽  
Slope Instability ◽  
Climate Factors ◽  
Cold Regions ◽  
The Past ◽  
Assessment Approach

Abstract This paper proposes an effective approach for evaluating the influences of climate change on slope stability in seasonally cold regions. Firstly, to semi-quantitatively assess the effects of climate changes on the uncertainty of climate factors, this study analyzes the trend of the two main climate factors (precipitation and air temperature) by the regression analysis using the meteorological monitoring data of the past 120 years in different scales (e.g., world, country (Japan), and city (Sapporo)), and the meteorological simulation data obtained by downscaling the outputs of three different regional atmospheric models (RAMs) with lateral boundary conditions from three different general circulation models (GCMs). Next, to discuss the effects of different climate factors (air temperature, precipitation, etc.) and to determine the key climate factors on the slope instability, an assessment approach for evaluating the effects of climate changes on slope instability is proposed through the water content simulation and slope stability analysis using a 2-dimensional (2D) finite element method (FEM) homogeneous conceptual slope model with considering freeze-thaw action. Finally, to check the effectiveness of the above assessment approach, assessment of instability of an actual highway embankment slope with the local layer geometry is done by applying the past and predicted future climate data. The results indicate that affected by global warming, the air temperature rise in some cold cities is more serious. The predicted future weather will affect the shape of the normal density curve (NDC) of the distribution of slope failures in one year. The climate changes (especially the increase in precipitation) in the future will increase the infiltration during the Spring season. It will lengthen the time that the highway slope is in an unstable state due to high volumetric water content, thereby enhancing the instability of the slopes and threatening more slopes in the future.

Experience with Interface Shear Box Testing for Pipe-Soil Interaction Assessment on Sand

2021 ◽  
Author(s):  
Zack Westgate ◽  
Ricardo Argiolas ◽  
Regis Wallerand ◽  
Jean-Christophe Ballard
Keyword(s):  
Soil Properties ◽  
Normal Stress ◽  
Oil And Gas ◽  
Early Stage ◽  
Soft Clay ◽  
Interface Roughness ◽  
Coarse Grained ◽  
Interface Shear ◽  
Shear Box ◽  
Test Database

Abstract This paper is a companion paper to OTC 28671, titled "Experience with Interface Shear Box Testing for Axial Pipe-Soil Interaction Assessment on Soft Clay", and presents a similar range of experience and best practice recommendations for geotechnical laboratory testing to determine soil properties relevant to pipeline-seabed friction on sandy seabeds. The paper is underpinned by a new database that demonstrates the driving parameters that influence interface friction in granular materials. By accurately quantifying shear resistance along the pipe-soil interface under low normal stresses imposed by subsea pipelines, design ranges in friction can be narrowed and/or tailored to specific pipeline conditions. These improved geotechnical inputs to pipe-soil interaction can alleviate unnecessary axial expansion mitigation and lateral stabilization measures, unlocking cost savings otherwise unavailable through conventional testing. A large database is presented, compiled from both previously published research and unpublished recent industry experience with low normal stress interface shear testing using various modified direct shear box devices. The test database comprises several coarse-grained soil types of both silica and carbonate minerology tested against pipeline coatings of various material, hardness and roughness. The database populates a framework for assessing frictional pipe-soil interaction response, illuminating key trends from normal stress, interface roughness and hardness, and particle angularity, which otherwise remain elusive when examined through individual test datasets. This database and the populated framework provides guidance to pipeline and geotechnical engineers in the form of a basis for initial estimates of axial and lateral friction of pipelines on sand and an approach for improving these estimates via focused site-specific testing. The test database includes previously unreleased project data collected over the past few years for offshore oil and gas projects. Similar to its predecessor paper on soft clays (OTC 28671), this paper shares the authors’ collective experience providing guidance on the planning, execution and interpretation of low stress interface shear tests in sands. The combined databases across both papers provide a significant improvement in early stage guidance for characterization of geotechnical soil properties for subsea pipeline design.

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