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This paper presents a geotechnical study of a Champlain Sea clay landslide at Breckenridge, Quebec, Canada. Previous studies have interpreted the landslide as triggered by an earthquake occurred about 1020 cal years BP. The current study is to estimate the minimum ground acceleration required to trigger the landslide as part of an effort to further understand the earthquake. The study consists of field and laboratory testing and slope stability analysis. Considerable evidences are presented to understand the slope failure mechanism. The result indicates a minimum horizontal ground acceleration of 0.28 g occurred at the site. Most importantly, the paper provides a case history for better understanding landslide hazards associated with sensitive clay failures in the region. Particularly, the study finds that the landslide is a "flake" type failure as opposed to a retrogressive failure commonly perceived for Champlain Sea clay landslides. It brings to light the "flake" slide as an important factor to consider for improvement of the current predictive models for sensitive clay failures. It also shows that earthquake-triggered "flake" slide can be much larger than retrogressive failures in the same settings. The case history may therefore help as a reference for improved mitigative measures. [ABSTRACT FROM AUTHOR]

Unlike typical soils, sensitive clays undergo extensive post-peak strength degradation with increasing strain and finally disintegrate into a remolded liquid state. Realization of post-peak stress-strain behavior of sensitive clay up to large strains is vital in assessing large deformation problems such as landslides and mud flows. The conventional experimental approaches are uncertain about accurately determining the post-peak stress curve up to large strains (>100%) owing to rapidly increasing testing problems at increasing strains. This necessitates the exploration of an alternative scientific approach to predict the complete stress-strain curve for sensitive clays, which is addressed in this paper. Post-peak stress-strain curves of sensitive clays for different sites are obtained by converting remolding index vs. strain energy curves. Using site-specific data from eastern Canada sites, a mathematical expression is proposed to predict the complete stress-strain curve. Subsequently, an equation is developed for predicting remolding energy based on the stress-strain curve. Finally, it is observed that the post-peak stress-strain behavior is highly site-specific and can be mathematically expressed with a combination of exponential and linear strain-softening curves. Overall, the knowledge of the complete stress-strain behavior contributes greatly to the prediction of post-failure movements closer to reality. • Determination of complete post-peak behavior of sensitive clays up to remolding. • Limitations of the generalized application of existing strain softening equation. • The proposition of a new site-specific strain softening equation with its application in some real-case scenarios. • The proposition for an equation to determine remolding energy as well as an equation to estimate the retrogression distance. [ABSTRACT FROM AUTHOR]

The main objective of this paper was to study the swelling properties of Regina clay. The deposit comprises a topsoil (surface to 0.3 m depth), an expansive clay (0.3-8 m), and a bottom till (8-9 m). High liquid limit (70 ± 15 %) and plastic limit (33 ± 4 %) indicated high water retention and adsorption capacity for the clay. Irrespective of the cover type (vegetation and cracked road), the field water content in summer closely matched the plastic limit. The clay was characterized by medium-to-high swelling that was best predicted by SP = 0.16 ( I). The soil had 51 % clay minerals including smectite (32 %), illite (7 %), kaolinite (5 %), and chlorite (3 %). With a CEC of 40 cmol(+)/kg, Ca and Mg were found to be the main exchangeable cations: the specific surface area was 50 m/g. The SP and P for a 1.2 m deep sample measured 12 % and 260 kPa, respectively, and the estimated surface heave of 180 mm gradually diminished to 3.6 m depth. These values matched well with consistency-based correlations. [ABSTRACT FROM AUTHOR]

Sensitive clay subjected to cyclic loading may experience gradual loss of its shear strength, which may lead to liquefaction. Foundations built on this clay would suffer extensive settlement and significant loss of bearing capacity or perhaps catastrophic failure. This paper presents an experimental investigation on sensitive (Champlain) clay obtained from the city of Rigaud, Quebec (Canada). Consolidation tests, static and cyclic undrained and drained triaxial tests were performed on representative samples of this clay. The objective of this investigation was to examine the influence of the physical and mechanical parameters, which govern the shear strength of sensitive clay subjected to cyclic loading. Based on the results of the present investigation and those available in the literature, it can be reported herein that the undrained response is the most critical for these foundations; furthermore, the preconsolidation pressure is considered as an important parameter in establishing the shear strength of sensitive clay. A design procedure is developed to determine the safe zone for the undrained and drained responses, within which a combination of the cyclic deviator stress and the number of cycles for a given soil/loading/site conditions can achieve a quasielastic resilient state without reaching failure. The proposed design procedure is applicable to all regions around the world, where sensitive clays can be found. Furthermore, this procedure can be adopted to examine the conditions of existing foundations built on sensitive clay at any time during its lifespan. [ABSTRACT FROM AUTHOR]

Several oil sands mines and refineries are currently recovering oil from the Athabasca River region near Fort McMurray, Alberta. Planning and construction of additional oil sands mines are in various stages of completion. Due to environmental concerns for aquatic life in areas downstream from current and future oil sands activities, surveys were conducted between 1998 and 2000 to determine whether the quality of water and sediments in tributaries of the Athabasca River are affected by flowing through reaches with exposure to natural oil sand deposits. This paper presents the results for metals in bed and suspended sediments collected from the Mackay, Steepbank, and Ells rivers during those surveys. The suspended sediments had a clay content (n = 7) ranging from 36.2% to 65.0%, while bed sediments, which consisted of a predominant sand fraction, had percent clay (n = 39) ranging from 0.0% to 38.1%. A Mann-Kendall non-parametric analysis to assess the longitudinal trend of the metals in the bed sediments found no significant (α = 0.05) downstream trend in the Mackay or Steepbank rivers; however, the Ells River displayed a generally decreasing tend from upstream to downstream. The results provide no indication that metal concentrations in the bed sediments and/or suspended sediments of the Mackay, Steepbank, and Ells rivers increase significantly as the three tributaries flow through reaches that have natural oil sand exposures (McMurray Formation). [ABSTRACT FROM AUTHOR]

The Tunnel Sealing Experiment (TSX) was an international project developed by Canada, Japan, France, and the United States. The TSX consisted of a clay bulkhead and a concrete bulkhead. The two bulkheads were at opposite ends of a 12-m-long sand-filled chamber. The heating phase involved the circulation of heated water through the TSX chamber to raise the temperature of the sealing system. This was done to evaluate the influence of elevated temperature on the performance of the bulkheads. Numerical analyses to simulate the thermohydromechanical evolution of the clay bulkhead and the surrounding rock of the TSX were performed using MOTIF finite-element program and compared with measured data. This paper focuses on a preliminary interpretation of the results from the fully coupled thermohydromechanical modeling of the clay bulkhead and the adjacent rock during heating. Discussion of the issues that will affect the ability to model a field application is provided in the course of comparing simulated and measured results. [ABSTRACT FROM AUTHOR]