Design and construction of a combination soil and water cover on a tailings storage facility in Tasmania

Authors: Cahill, C; Longey, R; Tonks, D Download Paper Open access courtesy of:

DOI https://doi.org/10.36487/ACG_repo/2215_83

Cite As:
Cahill, C, Longey, R & Tonks, D 2022, 'Design and construction of a combination soil and water cover on a tailings storage facility in Tasmania', in AB Fourie, M Tibbett & G Boggs (eds), Mine Closure 2022: Proceedings of the 15th International Conference on Mine Closure, Australian Centre for Geomechanics, Perth, pp. 1131-1138, https://doi.org/10.36487/ACG_repo/2215_83



Abstract:
The Main Creek Tailings Dam (MCTD), located at Grange Resources Pty Ltd’s (Grange) Savage River Mine in northwest Tasmania, has been in operation since 1985 and is transitioning from an operational tailings storage facility (TSF) to closure. The MCTD is an upstream constructed facility with a maximum height of approximately 83 m. Tailings stored in the MCTD are potentially acid forming (PAF) and require careful management through operation and closure to minimise the risk of the acid and metalliferous drainage (AMD) forming in the TSF. The site is situated on the west coast of Tasmania, with rainfall significantly exceeding evaporation. Therefore, a water cover would typically be most suitable; however, due to the upstream constructed embankments, a soil cover is required adjacent to embankments to meet long-term stability requirements. During operations, three trial covers were constructed and instrumented to monitor the performance over a number of years. The information obtained was used to evaluate cover performance and calibrate numerical transient seepage models. The preferred cover based on the trial cover performance was a combination clay and rockfill cover that maintained a high degree of saturation in the clay, minimising oxygen ingress to the underlying tailings, thus reducing the likelihood of AMD formation. The preferred clay and rock combination cover was assessed and optimised during the detailed design phase by undertaking two-dimensional transient unsaturated seepage modelling in SVFlux, considering a conservative climate scenario. Construction of the clay component of the combination cover has recently been completed. The construction process, challenges and QA/QC are discussed in this paper.

Keywords: tailings, AMD, closure cover modelling, closure planning

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