Daliri, F, Kim, H, Simms, P & Sivathayalan, S 2012, 'Contribution of desiccation to monotonic and cyclic strength of thickened gold tailings – not the same as over-consolidation', in R Jewell, AB Fourie & A Paterson (eds), Proceedings of the 15th International Seminar on Paste and Thickened Tailings
, Australian Centre for Geomechanics, Perth, pp. 73-83, https://doi.org/10.36487/ACG_rep/1263_07_Daliri
In many jurisdictions, regulators are concerned with remobilisation of high unbounded deposits of mine waste residuals, such as thickened tailings stacks. Consequently, the monotonic and cyclic behaviour of thickened tailings is of significant interest to practitioners of mine waste geotechnique. Thickened tailings are known to gain strength through a combination of hindered settling, desiccation, and consolidation post-deposition. This paper reports on the effects of over-consolidation ratio (OCR) and desiccation, investigated using a simple shear apparatus (NGI type). Samples for element testing were obtained from laboratory tests simulating multilayer deposition in columns or flumes. In each test, tailings were deposited at some initial solids concentration and allowed to desiccate to different values of water content, both above and below the shrinkage limit. These tailings were then overlaid with fresh tailings, and allowed to resaturate by capillary action from the fresh layer. Tailings from the bottom layer were then extracted using thin-wall Shelby tube. Some tailings were allowed to settle, subsequently extracted with no desiccation, and mechanically over-consolidated. Very sharp differences in both the quantitative and qualitative behaviours of samples prepared by these two methods were observed. Mechanically over-consolidated samples exhibited high peak strengths, whereas desiccated samples exhibited much lower strengths at phase transformation, but substantial strain hardening past phase transformation. This information is very important to geotechnical practitioners working on thickened tailings projects, as many operate under the assumption that desiccation is analogous to mechanical over-consolidation.
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