SECONDARY COMPRESSION OF A COHESIVE SOIL IN NORTHERN ONTARIO: A CASE STUDY

André Bom, J.Paul Dittrich, Matthew Thibeault, Greg Qu, Keli Shi, Tony Sangiuliano

In the proceedings of: GeoQuébec 2015: 68th Canadian Geotechnical Conference & 7th Canadian Permafrost Conference

Session: Soil Mechanics I / Mécanique des sols I

ABSTRACT: Long-term field settlement data and short-term and long-term laboratory consolidation test data provide a comparison of typical values used in the assessment of secondary compression (creep) of a cohesive soil beneath a highway embankment crossing a swamp area south of Sudbury in Northern Ontario. Design of the approximately 10 m high embankment with surcharge over an approximately 23 m thick clay deposit was based on the standard Terzaghi primary and secondary compression concepts. The secondary compression design parameters, which are the focus of this paper, were based on standard 24 hour load increment, one-dimensional laboratory consolidation tests and embankment construction included wick drains, staged construction and a surcharge. Regular monitoring of the consolidation of the cohesive layer using Settlement Rods (SRs), Vibrating Wire Piezometers (VWPs) and deep settlement Profilers (PRs) was carried out during embankment construction and surcharge period and annual readings have been taken following completion of the highway and opening to traffic in 2009. Secondary compression indices back-calculated from the long-term, post-construction field data are compared to values derived from the short-term (standard) laboratory consolidation tests as well as from long-term laboratory consolidation tests that have been running for about 1.5 years.

RÉSUMÉ: Les données de terrain du tassement à long s autoroute qui traverse un marécage au sud de la ville de Sudbury dans le nord de -23 m a été basée sur les concepts de compression primaires et secondaires standards de Terzaghi. Les paramètres de conception de la compression secondaire, sujet du présent article, ont été basés sur des essais de consolidation standard avec incrément de charge aux 24 heures; de la mise en place du remblai incluant les drains verticaux; de la construction par étapes; et une surcharge. Un suivi régulier du tassement de la couche de sol cohésif en utilisant les tiges de tassement, piézometres à corde vibrante et sonde de tassement de type Sondex (Slope Indicator) a été effectué pendant la période de construction à la circulation en 2009. Les indices de compression secondaires déterminés rétroactivement à partir de ces données recueillies post-construction sont comparés aux valeurs dérivées des résultats des essais de consolidation en laboratoire (court-terme) ainsi que des valeurs obtenues des tests de laboratoire de consolidation à long terme en cours depuis une année et demie.

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