The influence of slurry density on in situ density

Abstract

Since the beginning of the Paste and Thickened Tailings seminar series, there has been ongoing discussion as to whether an increase in the deposited (initial) slurry density will result in an increased density at depth within an accreting deposit, all else being equal. Despite frequent speculation and theorising, there has been relatively little laboratory data or other evidence presented at the conference series to address this question. To address the above deficiency, a literature review was undertaken to identify experimental programs where the same material was prepared for soil testing from different initial slurry densities. Twelve such studies were identified, of which nine indicate that an increase in initial slurry density resulted in increased density at subsequent significant vertical effective stresses. Case studies presented on three tailings deposits are investigated, to assess the implications of the presented results on the potential for initial slurry density to influence in situ density. For many of the studies reviewed, there appears to be an indication that an increased initial slurry density resulted in an increased in situ density at significant vertical effective stresses. Finally, a series of consolidation tests were undertaken by the authors, wherein four tailings types were prepared from different non-segregating initial slurry densities. For three of these materials, a dependence on situ density was observed, based on changes to initial slurry density. On the basis of the review and experimental data presented in this study, the authors conclude that for at least some materials, initial slurry density can result in an increased density across a wide range of vertical effective stresses.

A geological principle for the density of thickened tailings

“… Even for the same preparation method in the laboratory, pouring slurries of different (non-segregating) densities into consolidation test devices can also, in some cases, result in different non-converging NCLs. After a surprisingly long debate at various Paste and Thickened Tailings series seminars, this point was made clear by a literature review and further testing presented by Reid and Fourie (2015).…”

Estimating the in situ state of a thickened tailings deposit

“…This different range of achievable densities from different laboratory test methods has frequently been observed in low plasticity sandy materials (Ishihara 1993;Jefferies & Been 2000). Indeed, even different non-segregating slurry densities have been observed to result in different NCLs for some materials (Reid & Fourie 2015).…”

Stability of a proposed steepened beach

“…This indicated that the material was likely to be denser than the critical state in situ, and hence exhibit dilative behaviour. Recent interpretation (Reid & Fourie 2015) of in situ testing undertaken within the material suggests that the realised in situ states are somewhat denser than predicted from the laboratory testing, potentially resulting from air drying effects. Seddon (2007) obtained a residual strength ratio of 0.05 by means of vane shear testing within a portion of copper tailings undergoing air drying.…”