SYMPOSIA PAPER Published: 01 January 1988
STP10327S

Progressive Failure in the Vane Test

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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.

Author Information

DeAlencar, JA
The University of Alberta, Edmonton, Alberta, Canada
Chan, DH
The University of Alberta, Edmonton, Alberta, Canada
Morgenstern, NR
The University of Alberta, Edmonton, Alberta, Canada
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Developed by Committee: D18
Pages: 150–165
DOI: 10.1520/STP10327S
ISBN-EB: 978-0-8031-5030-0
ISBN-13: 978-0-8031-1188-2