Liu, M, Ganeson, T & Harrington, C 2024, 'Single-phase or two-phase? The impact on tailings dam breach modelling and impact assessment', in AB Fourie & D Reid (eds), Paste 2024: Proceedings of the 26th International Conference on Paste, Thickened and Filtered Tailings, Australian Centre for Geomechanics, Perth, pp. 235-246, https://doi.org/10.36487/ACG_repo/2455_19
(https://papers.acg.uwa.edu.au/p/2455_19_Liu/)
Abstract: Historically, dam breach analysis for tailings dams with supernatant ponds has used a single-phase approach, considering the breach flow as a mix of supernatant water and tailings, both eroded and liquefied due to lateral unloading. This flow mixture is typically modelled as a non-Newtonian fluid. The rheological properties are usually defined by the average solid concentration calculated using the estimated pond and tailings discharge volumes. In contrast, the two-phase modelling approach is a newer method that treats the breach in two separate stages: the initial release of supernatant water with eroded materials forming an initial flood wave, followed by the discharge of flowable tailings from liquefaction or slumping. The latter tends to have higher solid content and consequently deposits closer to the facility.
Although high density thickened tailings facilities operate with minimal supernatant water, they are usually designed with a storm storage allowance mandated by design codes. Therefore, it is necessary to assume a significant supernatant pond volume when considering flood-induced failure for this type of facility when doing dam breach analysis. For modelling assessment of the flood-induced breach, the choice between singlephase and two-phase approaches would significantly affect the modelling outcomes, as the solid content approaches that of high density thickened tailings, slight variations in solid content can lead to significant changes in the rheological properties.
This paper presents a case study where both single-phase and two-phase approaches were applied to a hypothetical high density thickened tailings storage facility. The study aims to investigate the differences in modelling outcomes and their implications on the dam breach impact assessment and highlight the importance of selecting appropriate modelling approaches for this type of facility.

Keywords: tailings dam breach analysis, high density thickened tailings, two-phase, rheology, impact assessment, non-Newtonian fluid