Historical tailings impoundments may contain saturated semi-fluid materials at depth, long after tailings deposition has ceased and after surface reclamation has been completed. These saturated materials can liquefy and flow if the impoundment is breached. A historical tailings pile can represent a risk to an underground mine development if there is potential for the mine development to generate a propagating zone of cracking and/or surface subsidence that ultimately interacts with the historical tailings impoundment. The risk of a sudden mudrush breach can be mitigated by reducing the potential for the tailings to flow. This paper presents a case study for the New Afton Mine located in British Columbia, Canada. A rheological model was developed to characterize the yield stress and flowability of a historic tailings deposit. In-situ and laboratory testing was completed to understand the variability between sandy tailings, deposited as above or below water beaches, and finer tailings ‘slimes’, deposited further from the deposition points. Simple index properties such as moisture content and clay-sized fraction were used to characterize the tailings rheology. A field-scale trial program was implemented to demonstrate that the tailings could be quickly and effectively densified and dewatered using wick drains, consolidation loading, and dewatering wells.
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