A geological principle for the density of thickened tailings

Reid, Donald B.; Jefferies, M. G.

doi:10.36487/acg_rep/1805_09_reid

Cited by 3 publications

(2 citation statements)

References 9 publications

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“…The CSL measured using moist tamped (MT) specimens is shown along with the range of consolidated densities achieved from 10 tests on intact specimens trimmed from blocks. These are seen to 'straddle' the CSL, exactly consistent with the observations of Reid & Jefferies (2018) with respect to the likely states of such deposits. Conversely, the SD triaxials carried out achieve significantly denser states than appear realistic for in situ conditions.…”

Section: Comparison To In Situ Densitiessupporting

confidence: 83%

Some considerations when preparing thickened tailings for shear strength testing in the laboratory from a slurry

Reid¹,

Fanni²,

Fourie³

2021

Proceedings of the International Seminar on Paste and Thickened Tailings

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Preparation of tailings in the laboratory to simulate the likely range of densities and resulting behaviour that will occur under load in situ is challenging. A number of issues of relevance include whether effects such as subaqueous deposition can be reproduced at all in the laboratory, and the potential importance of in situ layering of segregating tailings. These issues may have (thus far, largely unquantified) effects on mechanical behaviour in ways that are difficult to predict with element tests that are usually intentionally prepared homogeneously. Thickened tailings testing is conceptually easier, as issues such as segregation and the potential for subaqueous deposition are often not relevant. Despite this relative simplicity, a number of important considerations remain. While it is trivial to pour a thickened slurry into various forms of moulds or vessels to prepare for element testing, questions remain over whether the density that is reproduced will be relevant to in situ conditions. In particular, preparation of triaxial samples from thick slurries is particularly challenging as a number of steps are required to enable such samples to be 'free-standing', with each one of these steps potentially leading to slight disturbance and thus densification of the sample. Where such densification occurs, it would result in the element test results being non-conservative. This could have important implications with respect to expectations of the contractive (and potentially liquefiable) or dilative response of the tailings in situ.To investigate these issues, a series of slurry-deposited triaxial tests was carried out using a non-segregating slurry. As test methods were refined during the program, the amount of disturbance applied to the specimen was reduced. However, comparison of the triaxial tests to slurry consolidometer tests indicated that, regardless of efforts made, the triaxial tests achieved denser states at a given amount of consolidation stress. This was found to be the case using any conceivable range of assumed geostatic stress ratio to interpret the slurry consolidometer results. This outcome is speculated to be a result of the quiescent conditions used in the preparation of a slurry consolidometer specimen, which only requires pouring and then application of vertical load, first using weights, then a load frame. The implications of the increased density seen in triaxial tests compared to the likely more realistic value seen from the slurry consolidometer are discussed. Alternative preparation methods to target this looser density range are briefly discussed.

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Section: Comparison To In Situ Densitiessupporting

confidence: 83%

Some considerations when preparing thickened tailings for shear strength testing in the laboratory from a slurry

Reid¹,

Fanni²,

Fourie³

2021

Proceedings of the International Seminar on Paste and Thickened Tailings

Self Cite

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show abstract

“…The Plewes Method indicates a quite loose state within the sampled depth range of 7.0 to 8.8m, with Ψ values of +0.10 to +0.20. This is consistent with this area having historically undergone subaqueous deposition, which tends to result in extremely loose states (Shuttle and Cunning 2007;Reid and Jefferies 2017;Reid et al 2018;Reid et al 2019). Outside of this particular zone of subaqueous deposition, Ψ ranges between about -0.05 and +0.10, which is a range more consistent (e.g.…”

Section: Cpt Interpretationsupporting

confidence: 82%

The effect of tamping conditions on undrained shear strengths of a non-plastic sandy silt tailings

Reid

Fanni

DiDonna³

2022

Can. Geotech. J.

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A series of direct simple shear (DSS) tests were carried out on a non-plastic sandy silt lead−zinc−silver tailings to develop a relationship between undrained shearing behaviour and density for contractive states. The critical state line was also obtained through triaxial compression tests to enable the DSS tests to be viewed in a critical state framework and allow comparison with in situ testing. It was found that the gravimetric water content (GWC) used to tamp the specimens had a significant effect on the resulting undrained strengths when attempting to achieve dense states — with higher GWC giving lower strength at a given density than a lower GWC. Intact and slurry deposited (SD) samples were also tested to access denser states without inducing tamping-related stresses. These showed a more consistent trend with the loose-tamped specimens, and with other data from the literature. Plausible explanations as to the causes of the increased strength of dense-tamped samples were obtained through estimating potential preconsolidation stresses and “locked in” horizontal stresses that may occur from dense tamping. The importance of these observations on the development of density−strength profiles in engineering practice was outlined.

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CPTu-Based Spatial Variability Assessment of Thickened and Conventional Mine Tailings

Macedo,

Vergaray,

Liu

et al. 2024

J. Geotech. Geoenviron. Eng.

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A geological principle for the density of thickened tailings

Cited by 3 publications

References 9 publications

Some considerations when preparing thickened tailings for shear strength testing in the laboratory from a slurry

Some considerations when preparing thickened tailings for shear strength testing in the laboratory from a slurry

The effect of tamping conditions on undrained shear strengths of a non-plastic sandy silt tailings

CPTu-Based Spatial Variability Assessment of Thickened and Conventional Mine Tailings

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