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Partial Drainage Effects during Vane Shear Tests, with an Emphasis on the Measurement of Remoulded Strengths

Tailings and Mine Waste Conference (2023 : Vancouver, B.C.); University of British Columbia. Norman B. Keevil Institute of Mining Engineering

The measurement of peak and remoulded shear strength, and the post-peak reduction in strength with strain, of contractive tailings is undergoing increased focus based on recent prominent tailings storage facility (TSF) failures and subsequent industry guidance. One tool that offers benefits in this area is the vane shear test (VST) as it measures shear strengths directly in situ in a relatively undisturbed state and can directly measure aspects of post peak softening to larger strains than most common laboratory tests. However, for the data from a VST to be useful, it must be unambiguously measuring undrained shear strengths without appreciable drainage occurring during the test. Despite this clear necessity, as most VST standards are focused on predominately low permeability clay soils, arguably insufficient attention and details related to drainage issues is included in the currently available standards – particularly post-peak, where significant time may be required to reach a remoulded strength, increasing the risk of partial drainage. This issue is exacerbated by a lack of consensus as to which analytical framework is most suitable to quantify the potential onset and magnitude of drainage. To provide additional data to assist in the quantification of drainage during the VST, and to highlight the issue generally, this paper presents the results of a series of VST carried out in a predominately siltsized iron ore tailings. The consolidation characteristics of the material are such that use of “standard” VST rotation rates appeared likely to result in pre-failure drainage affecting strengths recorded by the VST. As such, a range of rotation rates and methods were applied to investigate the onset of drainage, with particular focus on post-peak conditions. The data suggests that drainage may be inhibiting the observation of strain softening of the tailings. The two available methods to infer drainage acting on a VST agree reasonably with the results of the data presented here.

Text

2023-12-08

Attribution-NonCommercialNoDerivatives 4.0 International

http://hdl.handle.net/2429/86797

Unreviewed

http://creativecommons.org/licenses/by-nc-nd/4.0/