STP483: Loss of Strength Due to Sampling in a Glacial Lake Deposit

    Adams, JI
    Supervising engineer and engineer, Hydro Electric Power Commission of Ontario, Toronto, Ont.

    Radhakrishna, HS
    Supervising engineer and engineer, Hydro Electric Power Commission of Ontario, Toronto, Ont.

    Pages: 12    Published: Jan 1971


    Abstract

    Large discrepancies between the undrained strength values measured by in situ vane and those measured by laboratory triaxial tests on tube samples, in a glacial lake deposit, are analyzed in terms of changes in effective stress during the sampling process. Data are presented to show that even in a relatively insensitive and reworked clay, significant loss in strength can occur due to the stress release effects of sampling at depth. The loss of strength is attributed to the loss of suction which occurs during sampling. Reconsolidating an undisturbed specimen to its estimated in situ vertical stress under Ko condition or to an equivalent isotropic stress, before running an undrained test, is shown to yield correct in situ strength, of a normally consolidated clay. A method of correcting for conventional undrained testing is proposed based on the computed loss of suction as related to change in moisture content due to swelling.

    Keywords:

    shear strength, sampling, suction, glacial deposits, in situ, strength, anisotropy, consolidation, pore pressure behavior, evaluation, tests


    Paper ID: STP26662S

    Committee/Subcommittee: D18.02

    DOI: 10.1520/STP26662S


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