Plastic anisotropy and destructuration of soft Finnish clays

Mirva Koskinen

    Research output: ThesisDoctoral ThesisCollection of Articles

    Abstract

    Due to growth of population, there is a need to construct on areas on soft soils. Therefore, there is also a need for tools for modelling deformations of soft soils. Soil models called S-CLAY1, accounting for fabric anisotropy, and S-CLAY1S, accounting additionally for bonding and destructuration, were developed. Aim of this work was to design and perform a comprehensive series of laboratory tests in order to validate the S-CLAY1 and S-CLAY1S models. Four typical soft Finnish clays were chosen for test materials. The clays were Otaniemi clay from Espoo, POKO clay from Porvoo-Koskenkylä motorway site, Murro clay from Seinäjoki and Vanttila clay from Espoo. These clays represent a typical variety of moderately to highly sensitive clays. The sensitivity is a demonstration of interparticle bonding of natural clays. The series of tests included tens of triaxial tests on both reconstituted and natural samples. In tests on reconstituted samples, anisotropy can be studied in the absence of bonding. Natural clays, however, exhibit anisotropy and bonding. The triaxial tests were consolidation tests with different stress ratios, and drained and undrained shear tests. Additionally, oedometer tests and index tests were carried out. The behaviour of Murro test embankment was also calculated with the two models. Model parameters for S-CLAY1 and S-CLAY1S models were determined from the test data, and the test results were simulated as single element simulations. The simulations showed that accounting for anisotropy enhanced the predictions of tests on reconstituted samples significantly compared to predictions with an anisotropic model. Using certain parameter values, the anisotropic S-CLAY model could also be used for satisfactory predictions of tests on natural samples, but, however, using the destructuration law incorporated in the S-CLAY1S model, the predictions could be improved further. The behaviour of Murro test embankment was also modelled rather realistically using the S-CLAY1S model compared to observations of settlements and horizontal displacements. S-CLAY1 and S-CLAY1S do not account for rate effects or elastic anisotropy, but despite of that, the models are a promising tool for geotechnical design and a basis for model development in the future.
    Translated title of the contributionPehmeiden suomalaisten savien plastinen anisotropia ja rakenteen vaikutus
    Original languageEnglish
    QualificationDoctor's degree
    Awarding Institution
    • Aalto University
    Supervisors/Advisors
    • Korkiala-Tanttu, Leena, Supervising Professor
    • Karstunen, Minna, Thesis Advisor, External person
    Publisher
    Print ISBNs978-952-60-5928-0
    Electronic ISBNs978-952-60-5929-7
    Publication statusPublished - 2014
    MoE publication typeG5 Doctoral dissertation (article)

    Keywords

    • soft clay
    • anisotropy
    • destructuration

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