Reid, D & Boshoff, J 2015, 'Stability of a proposed steepened beach', in R Jewell & AB Fourie (eds), Paste 2015: Proceedings of the 18th International Seminar on Paste and Thickened Tailings, Australian Centre for Geomechanics, Perth, pp. 181-194, https://doi.org/10.36487/ACG_rep/1504_12_Reid
(https://papers.acg.uwa.edu.au/p/1504_12_Reid/)
Abstract: Existing topography at an operational lateritic nickel facility is such that if the tailings beach slope could be increased to 1-2% for approximately one year, significant costs related to wall building could be deferred. As additional thickening capacity would require significant capital expenditure, polymer treatment technologies have instead been investigated.
As part of the trial process for polymer treatment, the stability of the potential steepened beach was assessed. While beach slopes of the range targeted here would, for many materials, be unlikely to produce an unstable landform, lateritic nickel tailings develop very low dry densities, consolidate slowly, and contain hypersaline pore fluid. This combination results in a lower resistance to slope instability, all else being equal. Further, polymer treatment technologies, while providing benefits through rapid dewatering and beach slope development, have been shown to result in an increased brittleness for some materials.
Laboratory characterisation of the polymer treated material was first undertaken, by means of (i) monotonic, cyclic and post-cyclic simple shear testing, to assess the potential for strength loss of the material, (ii) laboratory-scale shear vane testing, to estimate residual shear strength, and, (iii) settling and consolidation tests, to provide input to consolidation modelling.
A consolidation model of the proposed steepened beach was then developed. Outputs from this model were used as the basis for infinite slope stability analyses on a variety of scenarios. It was found that over the one year planned deposition period, beach slopes of 1.5% or less are likely to result in a satisfactory factor of safety (FS) for the steepened beach.