Cam-clay Material Properties for Soft Holocene and Pleistocene clay deposits in Northern Alberta

H. Karimpour, A. Eshraghian, D.E. Becker, M. Etezad, R. McNally

In the proceedings of: GeoRegina 2014: 67th Canadian Geotechnical Conference

Session: Soil Mechanics

ABSTRACT: A well-instrumented 20 m high embankment was constructed on clayey and silty Holocene and Pleistocene deposits in Northern Alberta. The embankment construction provided an opportunity to use the instrumentation and laboratory test data to assess deformation properties of these deposits. A two-dimensional deformation analysis was performed using a finite element code (Plaxis 2D) and results were compared with the instrumentation data to calibrate (field-match) the observed behaviour to evaluate the material properties. Cam-clay based constitutive models were used for modelling the behaviour of Holocene and Pleistocene clay deposits. Comparison of the field data and analysis results shows that the material parameters used for these models provide reasonably good agreement with the measured foundation displacements. The displacements within the Holocene clay deposit (Hl clay) are significantly greater than those observed within the Pleistocene clay layer. The amount of horizontal displacement within other foundation layers was in the range of 10% to 20% of the total lateral foundation deformation. This paper briefly describes the ground conditions, performed analysis and results. The assessed deformation material properties for the shallow Holocene and Pleistocene clay deposits are considered applicable to other similar deposits in Northern Alberta. RÉSUMÉ Une digue bien instrumentée à une hauteur de 20 m a été construite sur des dépôts argileux et limoneux de l'Holocène, ainsi que des dépôts du Pléistocène, au nord de l'Alberta. La construction de la digue a permis d'utiliser les résultats de l'instrumentation et des tests de laboratoire pour évaluer les propriétés de déformation de ces dépôts. Une analyse de la déformation à deux dimensions a été effectuée en utilisant un code d'éléments finis (Plaxis 2D) et les résultats ont été comparés avec les données d'instrumentation pour calibrer le comportement observé et pour évaluer les propriétés des matériaux. Des modèles Cam-clay ont été utilisés pour la modélisation du comportement des dépôts d'argile de l'Holocène et du Pléistocène. Une comparaison des données du terrain avec les résultats de l'analyse montre que les propriétés matérielles utilisées pour les modèles fournissent un accord raisonnable avec les déplacements de fondation mesurés. Les déplacements observés dans le dépôt d'argile Holocène sont considérablement plus grands que ceux observés dans le dépôt d'argile Pléistocène. Le déplacement horizontal dans les autres formations de la fondation était environ 10% à 20% de la déformation latérale totale de la fondation.Cet article présente une brève description des conditions du sol, des analyses effectuées et des résultats de l'étude. Les propriétés de déformation des dépôts peu profonds d'argile de l'Holocène et du Pléistocène sont considérés applicables à d'autres dépôts semblables dans le nord de l'Alberta. 1 INTRODUCTION Large foundation deformations are expected when dealing with construction of earth structures on soft clay foundations. Tavenas and Leroueil (1980) analyzed a number of case histories and concluded that the clay foundation response to embankment construction is not truly undrained as is commonly assumed. Based on their findings, they provided revised methods for prediction of porewater pressure, stability conditions, and deformations (lateral displacement and settlement). Crooks et al. (1986) studied a high roadway overpass structure on soft clay that failed when it reached 12 m height. They used an effective stress approach to analyze the behaviour of soft clay foundation and porewater pressure response. It was suggested that the root causes of the failure were a limited understanding of the mass strength of the foundation material, caused by relying on small-scale field or laboratory testing and neglecting transitional failure modes. Hunter and Fell (2003) studied 13 well-monitored embankments up to 9.6 m high and constructed to failure on soft clay foundation. Based on the observed deformation behaviour and excess porewater response, the authors provided a guideline to identify the impending failure conditions and claimed that the onset of failure can be detected when embankments are at 70% to 90% of their failure height. This paper presents a calibration of the material properties of a well-instrumented 20 m high embankment constructed on clayey and silty Holocene and Pleistocene deposits in Northern Alberta. The site geology, embankment geometry, and the initial material properties are described. Numerical modelling is employed to calibrate the initially estimated material properties by comparing the numerical modelling results against those from instrumentation data. Finally, the calibration results are discussed and typical material properties are presented for the soft clay Holocene and Pleistocene deposits in Northern Alberta.

RÉSUMÉ: lay Material Properties for Soft Holocene

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Cite this article:
H. Karimpour; A. Eshraghian; D.E. Becker; M. Etezad; R. McNally (2014) Cam-clay Material Properties for Soft Holocene and Pleistocene clay deposits in Northern Alberta in GEO2014. Ottawa, Ontario: Canadian Geotechnical Society.

@article{GeoRegina14Paper354,author = H. Karimpour; A. Eshraghian; D.E. Becker; M. Etezad; R. McNally,title = Cam-clay Material Properties for Soft Holocene and Pleistocene clay deposits in Northern Alberta,year = 2014}