Rohde, T 2026, 'Scale effects in engineered cover design: lessons from Queensland mine sites', in AB Fourie, G Boggs, J Heyes & M Tibbett (eds), Mine Closure 2026: Proceedings of the 19th International Conference on Mine Closure, Australian Centre for Geomechanics, Perth, pp. 1-14, https://doi.org/10.36487/ACG_repo/2615_47
(https://papers.acg.uwa.edu.au/p/2615_47_Rohde/)
Abstract: Designing engineered covers for waste rock and tailings (mineralised waste) is essential for sustainable rehabilitation in Queensland’s North West Mineral Province. A significant challenge is reliably predicting how materials will perform at field scale over several decades, as laboratory-derived data often fails to reflect realworld conditions. This paper examines the critical role of scale effects in cover design, drawing on research and long-term monitoring data from two sites in North West Queensland.
At the laboratory scale, determining hydraulic properties like soil–water characteristic curves (SWCCs) is fundamental to design. However, reconstituted laboratory samples often overestimate water-holding capacity because they lack the in situ structure, stress history and cementation found in the field. Furthermore, the common omission of hysteresis in laboratory testing can lead to non-conservative predictions of cover efficiency.
Intermediate-scale column trials provide valuable comparative water balance data for assessing options like non-acid forming waste rock covers. While effective for side-by-side design comparisons and model calibration, these trials cannot fully replicate natural atmospheric variability.
The most robust validation comes from large-scale field trials, such as the decade-long program at a semiarid mine in North West Queensland. The field trials demonstrate that thick infiltration and storage layers, combined with reduced permeability layers, maintain low percolation rates even through extreme cycles of intense wet seasons and prolonged droughts. Integrating findings across these multiple scales, while acknowledging the limitations of each, enables the development of resilient covers capable of meeting longterm rehabilitation goals in challenging environments.