Deformation properties of highly plastic fissured Palaeogene clay - Lack of stress memory?

Anette Krogsbøll, Ole Hededal, Niels Nielsen Foged

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    Abstract

    The geological preconsolidation of the Palaeogene clays in Denmark is estimated to 5-8 MPa or more, whereas laboratory and field experiences indicate values between 100 and 3000 kPa. Presumably,
    the high plasticity clay loses its memory of earlier preloads due to swelling, or as an effect of fissuring or debonding. Based on a large amount of high quality tests on Palaeogene clay partly encountered at Fehmarn Belt the typical deformational behaviour during unloading and swelling is discussed and evaluated with focus on stress states. K0-OCR relations are established and the relations are evaluated based on the degree of debonding caused by natural processes insitu as compared to processes induced during severe loading and unloading in laboratory. A long term oedometer test on Lillebælt Clay with a series of loading and unloading cycles was carried out. The test results are used to evaluate deformation properties, and to help explain the large primary and secondary swelling indices measured in Palaeogene clays and how they are related to preconsolidation stress. It is proven that the Palaeogene clay tends to “forget” the preconsolidation stress and the consequence is that OCR is not always a suitable parameter to estimate deformation and strength parameters from, unless additional information on structure of the clay is included. This is not solved yet.
    Original languageEnglish
    Title of host publicationProceedings of 16th Nordic geotechnical meeting NGM 2012
    Volume1
    Publication date2012
    Pages133-140
    Publication statusPublished - 2012
    EventNordic Geotechnical Meeting - Tivoli Congress Center, Copenhagen, Denmark
    Duration: 9 May 201212 May 2012
    Conference number: 16
    http://www.ngm2012.dk/

    Conference

    ConferenceNordic Geotechnical Meeting
    Number16
    LocationTivoli Congress Center
    Country/TerritoryDenmark
    CityCopenhagen
    Period09/05/201212/05/2012
    Internet address

    Keywords

    • Clay
    • Consolidation
    • Creep
    • Laboratory tests

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