Influence of Salt Concentration on Shear Strength Behaviour of Leda Clay

M. Yary, A.A. Aldaeef, M.T. Rayhani

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

Session: Laboratory and Field Testing

ABSTRACT: of Salt Concentration on Shear Strength Behaviour of Leda Clay M. Yary, A.A. Aldaeef, M.T. Rayhani Department of Civil and Environmental Engineering Carleton University, Ottawa, ON, Canada ABSTRACT Leda clay is a highly sensitive soil formed through marine deposition of the Champlain Sea, and now covers major parts of eastern Ontario and Quebec regions in Canada. This soil can absorb and retain a large amount of water and, upon disturbance, can turn to quick clay. Observations have shown that quick clay may occur in sediments where salt concentration has been significantly decreased due to leaching. This paper describes results of an experimental research aimed at investigating the relationship between the shear strength of Leda clay and its salt content. Shear strength of undisturbed Leda clay samples with different salt concentrations were determined using unconsolidated undrained triaxial tests. Results indicate that the undrained shear strength of the test specimens decreased as the salt concentration decreased. However, the exposure to different salt solutions resulted in lower rates of shear strength reductions comparing to the samples that were washed with distilled water. RÉSUMÉ Argile à Leda est un sol qu'est très sensible formée par le dépôt marin de la mer de Champlain. Le sol maintenant couvre les régions principales de l'est de l'Ontario et du Québec dans Canada. Ce sol peut absorber et retenir une grande quantité d'eau et, si dérangé, peut rapidement tourner à l'argile. Les observations ont montré que l'argile rapide peut se produire dans les sédiments où la concentration en sel a été considérablement diminué en raison de la lixiviation. Ce document présente les résultats d'une recherche expérimentale qui a étudié la relation entre la résistance au cisaillement de l'argile à Leda et sa teneur en sel. La résistance au cisaillement de non perturbées échantillons d'argile à Leda avec différentes concentrations en sel ont été déterminer en utilisant des tests triaxial non consolidées. Les résultats indiquent que la résistance au cisaillement des échantillons d'essai diminue lorsque la concentration en sel diminue. Cependant, l'exposition à des solutions de sels différents conduit à des taux plus faibles de réduction de résistance au cisaillement de comparaison aux échantillons qui ont été lavés avec de l'eau distillée. 1 INTRODUCTION Natural disasters can cause deaths and significant damages to both infrastructure and the environment. In the case of environment, landslide effects resulting from soil failure can be extremely damaging, posing threats to human life, property and foundations. This paper presents the results of an experimental study on shear strength behaviour of Leda clay in Ontario and Quebec, Canada. Leda clay is mostly composed of clay and silt sized particles. The fine particles arrived from the Canadian Shield by glaciers and washed into the Champlain Sea (Lacasse, 2009). As the particles settled through the salty water, they became attracted to one another and formed loose clusters that then fell to the seafloor (NRCAN, 2008). The resulting sediment has strong structure that is capable of retaining a large amount of water (up to 80 percent of water) (Quigley et at. 1983). Once the heavy glaciers have retreated, they left a depression on the land, which was then flooded by the Atlantic Ocean, and as a result rock particles mixed with salty water to form a new inland sea. The sediment bonding is held together by salt crystals, and if those bonds are broken, they cannot be reformed (Lacasse, 2009). Once this bonding is leached, the clay gets weaker, but still water-rich as it holds around 80% of water content. Thus, if sufficiently disturbed in any way, it can liquefy and become quick clay (NRCAN, 2008). Therefore, the index properties of this soil are vital in controlling the stability of this soil. The index properties will also be important factors in exploring the injection of salt-water used for this research. This salt injection seems to increase the shear strength behaviour of the clay, and stabilize the layer of the soil that is subjected to liquefaction. This idea is explored here as a preventative measure to mitigate such damage. 2 LITERATURE REVIEW Studies have shown that the salinity of Leda clay at 15-20m depth has decreased from 7-15g/l to almost zero or 1g/l at the surface, indicating that salinity increases with depth (Quigley et al. 1983). Salinity becomes an important factor when a sensitive soil such as Leda clay is the subject soil. Sensitivity can be defined as the ratio of the undisturbed shear strength of the soil to its remoulded shear strength. It has been reported that the shear strength of Leda clay has an inverse relationship with sensitivity, where the increase of ion concentrations reduces the soil sensitivity (Locat, 1985). Sensitivity was also reported to be a function of the type of chemical ions. Dominant malevolent ions (e.g., sodium and potassium) were shown to result in a higher sensitive soil structure. However, as the ion valency increases to be multivalent (e.g., Ca2+ and Mg2+) and trivalent (e.g., Al3+), the

RÉSUMÉ: ence of Salt Concentration on Shear Strength Behaviour of Leda Clay M. Yary, A.A. Aldaeef, M.T. Rayhani Department of Civil and Environmental Engineering

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Cite this article:
M. Yary; A.A. Aldaeef; M.T. Rayhani (2014) Influence of Salt Concentration on Shear Strength Behaviour of Leda Clay in GEO2014. Ottawa, Ontario: Canadian Geotechnical Society.

@article{GeoRegina14Paper427,author = M. Yary; A.A. Aldaeef; M.T. Rayhani,title = Influence of Salt Concentration on Shear Strength Behaviour of Leda Clay ,year = 2014}