STP1014

    Progressive Failure in the Vane Test

    Published: Jan 1988


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    Abstract

    A finite-element analysis of the undrained vane test has been performed using an elasto-plastic constitutive relation with strain-softening behavior. A hyperbolic strain softening model has been developed to model the post peak behavior of the soil. This constitutive relationship assumes an elastic behavior up to peak strength, and the material subsequently softens according to a hyperbolic relationship. As a result one can model different rates of post peak softening in a compact manner while maintaining the same peak and residual strength. The results of the analysis show that the peak torque measured in a vane test depends not only on the peak strength and the residual strength of the material, but also that the rate of post peak softening has a dramatic effect on the peak torque and the torque-rotation relationship of the test. If the material possesses moderate rates of softening behavior, the maximum torque is close to the value calculated based on peak strength. In other words, the results of the vane test can be used to deduce the peak strength of the material. At high rates of softening, the progressive development of the failure zone results from stress concentration effects at the blades of the vane, and the strength is mobilized in a nonuniform manner around the vane at maximum torque. Therefore the distribution of stresses around the perimeter of the vane is not known and the assumption of uniform mobilization of shear strength will lead to an incorrect evaluation of the peak strength of the material. This effect is especially pronounced in very strain sensitive soils. The finite-element results also reveal a localized failure zone around the vane when the maximum torque is reached. Comparisons between the finite-element results and existing experimental studies of soil behavior around a vane are in agreement for the failure mechanism developed during a vane test.

    Keywords:

    vane tests, progressive failure, strain softening, finite-element analysis, plasticity


    Author Information:

    DeAlencar, JA
    Ph.D. student, assistant professor, and professor, The University of Alberta, Edmonton, Alberta

    Chan, DH
    Ph.D. student, assistant professor, and professor, The University of Alberta, Edmonton, Alberta

    Morgenstern, NR
    Ph.D. student, assistant professor, and professor, The University of Alberta, Edmonton, Alberta


    Paper ID: STP10327S

    Committee/Subcommittee: D18.03

    DOI: 10.1520/STP10327S


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