Geotechnical Characteristics of Leda Clay in the Ottawa Region

A. Drevininkas, M. Manzari, T. Sangiuliano, D. Staseff

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

Session: Expansive Soils

ABSTRACT: Near the end of the Late Wisconsinan glaciation the Ottawa area was inundated by the Champlain Sea resulting in the deposition of thick glaciomarine clay deposits. These clay deposits, known as Leda Clays, are well known as a sensitive clay with a low compression index up to its preconsolidation stress and a high compression index beyond this stress. The flocculated structure, mineralogy and porewater salinity of the clay results in a unique soil in Ontario that provides geotechnical challenges for design and construction. The Ministry of Transportation of Ontario has carried out hundreds of geotechnical investigations in the Ottawa Region within Leda Clay deposits since the 1950s for highway embankments and bridge structures. As part of these geotechnical investigations, soil properties were determined by laboratory and in situ testing. This paper presents a summary of the results of this testing and analysis to further characterize the compressibility characteristics of the Leda Clay. Correlations with some index soil laboratory test results are provided. RÉSUMÉ Vers la fin de la dernière glaciation Wisconsinienne, la région d'Ottawa était inondée par la mer de Champlain entraînant des dépôts épais d'argile glacio-marins. Ces dépôts d'argile, appelés argiles Léda, sont bien connus comme une argile sensible avec un indice de compression faible jusqu'à sa pression de préconsolidation et un indice de compression élevé au-delà de cette pression. La structure floculée, la minéralogie et la salinité des eaux interstitielles de l'argile résultent à un sol unique en Ontario qui donne des défis géotechniques pour la conception et la construction. Le ministère des Transports de l'Ontario a réalisé des centaines d'études des fondations dans la région d'Ottawa dans les dépôts d'argile Léda depuis les années 1950 pour les remblais routiers et des structures de pont. Dans le cadre de ces études des fondations, des propriétés physiques et mécaniques ont été déterminées par les essais en laboratoire et in situ. Cet article présente un résumé des résultats de ces essais et des analyses pour caractériser davantage les caractéristiques de compressibilité de l'argile Léda. Les corrélations avec certains indices du sol obtenus d'essais en laboratoire sont données. 1 INTRODUCTION The Ottawa Region is known to be underlain by highly sensitive marine clays of variable plasticity known as Leda Clay. Leda Clays are known to have a sharp change of compressibility at the preconsolidation pressure when the applied stress by man-made activities exceeds the preconsolidation pressure ('p). Due to the high increase of compressibility at 'p, this pressure is recognized by some as the yield point and used in establishing the yield envelope of Leda Clay (e.g., Tavenas & Leroueil 1977). There are few reliable correlations available for soil properties of Leda Clay that can be used to predict first order settlement in this deposit. Most published correlations in geotechnical literatures are for low to medium plasticity clays with low to medium sensitivity. These correlations tend to under predict settlements for the loads applied to Leda Clay. The compressibility characteristics of clays are typically determined by obtaining a limited number of relatively undisturbed samples and conducting laboratory oedometer (consolidation) testing to obtain soil parameters. These laboratory tests are expensive and time consuming. Correlation with quick and inexpensive index laboratory test results would provide a more cost effective and efficient method to assist with prediction of settlements in the preliminary stage of projects, as well as to calibrate in situ testing methods. Other options include profiling soil parameters for settlement analysis by carrying out in situ testing, such as piezocone penetration testing (CPTu). 2 GEOLOGY According to Bélanger (1998), the Ottawa Region is located near the southern boundary of the Grenville

RÉSUMÉ: chnical Characteristics of Leda Clay in the Ottawa Region

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Cite this article:
A. Drevininkas; M. Manzari; T. Sangiuliano; D. Staseff (2014) Geotechnical Characteristics of Leda Clay in the Ottawa Region in GEO2014. Ottawa, Ontario: Canadian Geotechnical Society.

@article{GeoRegina14Paper190,author = A. Drevininkas; M. Manzari; T. Sangiuliano; D. Staseff,title = Geotechnical Characteristics of Leda Clay in the Ottawa Region,year = 2014}