STP483

    Effect of Sampling and Testing Techniques on the Shear Strength of a Glacial-Lacustrine Clay from Welland, Ontario

    Published: Jan 1971


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    Abstract

    The “lower stratified” zone of the clay deposits at Welland, Ontario, is a sensitive lacustrine clay of medium to high plasticity. This zone is of particular importance in the stability of clay slopes for the deep approach cuts of the Townline Road/Rail Tunnel currently being constructed to pass beneath the relocated Welland Canal. The undrained shear strength is a minimum parallel to the bedding in certain critical layers within the lower stratified zone, indicating that the critical stability surface would include a long flat portion along this bedding. As the economy of the project demanded the steepest possible slopes, it was judged necessary to obtain and test the best possible undisturbed samples. Data available allow a comparison of test specimens obtained from block samples, and 5 and 3-in. tube samples. These data demonstrate the need for good undisturbed samples, geologically representative samples (the critical layers within the lower stratified zone), and relevant laboratory testing (measuring the shear strength parallel to the bedding).

    The paper raises two important points: (a) the degree to which the peak undrained shear strength obtained from tests on good undisturbed samples can be mobilized along a failure surface in a soil mass and (b) the effect on the shear strength of a weak layer in a stratified clay as a result of pore pressure equalization with adjacent dissimilar layers.

    Keywords:

    sampling, undisturbed samples, test shaft, block samples, tube samples, stratified clay, lacustrine clay, soil mechanics, undrained shear strength, anisotropy, strain rate, pore pressure equalization, progressive failure, evaluation, tests


    Author Information:

    Conlon, RJ
    Head, Geotechnical Department, and soil mechanics and foundation engineer, H. G. Acres Limited, Niagara Falls, Ont.

    Isaacs, RMF
    Head, Geotechnical Department, and soil mechanics and foundation engineer, H. G. Acres Limited, Niagara Falls, Ont.


    Paper ID: STP26656S

    Committee/Subcommittee: D18.02

    DOI: 10.1520/STP26656S


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