2022 – Designing tailings dams for closure

David J Williams – The University of Queensland, Brisbane, Australia

The requirement to design tailings dams for closure is not a new concept. The 2007 CDA Dam Safety Guidelines stipulated closure design for an “Extreme” Consequence Classification, as did the 2012 ANCOLD Tailings Dam Guidelines. This translates to a 1 in 10,000-year return period for flood and earthquake loadings. However, tailings dam design and construction has focussed to date on the operational phase of the facility, for which a less than Extreme Consequence Classification typically applies, with a return period for flood and earthquake loadings of typically 1 in 100 years or 1 in 1,000 years, corresponding to much lower loadings than 1 in 10,000 years. The closure requirement is relegated to future consideration and is, in many cases, never adequately addressed. The fatal Brumadinho tailings dam failure in 2019 led to the 2020 Global Industry Standard on Tailings Management, which had the aspirational goal of “zero harm to people and the environment”. This elevated the Consequence Classification to Extreme throughout the tailings facility life cycle, and hence the loading return period to 1 in 10,000 years. While it could be argued that an Extreme Consequence Classification may not be warranted for many tailings dams, it is difficult to remove all “credible” failure modes in perpetuity, and hence it is difficult to design tailings dams for closure. Tailings dams should be designed for closure from the outset.

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