Centrifuge modelling of drawdown seepage in tailings storage facilities

Uncertainties surrounding seepage behaviour are a key issue raised in tailings storage facility (TSF) operation. Poor seepage management can result in negative environmental impacts, costly remediation or even embankment failure and, in the context of mine closure, long term liabilities and/or legacy site issues. In particular, recovery pumping rates must be maintained for sufficient time to capture seepage both during operation and after closure during reservoir drawdown.
Seepage analyses for TSF design commonly assume isotropic or, at best, anisotropic homogeneous material properties. However, layering during deposition, consolidation and swelling on drying and wetting create a seepage environment far more complex than these assumptions suggest. Improved modelling is required to increase analysis confidence.
Centrifuge modelling allows geotechnical phenomena to be investigated using scale models under representative stress conditions. However, few previous examples exist for seepage modelling using this technique. This paper briefly discusses modelling equipment development for use with the UWA beam geotechnical centrifuge. Results for seepage during reservoir drawdown, simulating facility closure, are then presented for a layered, heterogeneous embankment model, as compared to predictions made by commercial analysis software. Findings are used to comment on the implication of simplifying analysis assumptions on drawdown time and flowrate calculations.