Capping design for 2 tailings storage facilities with unique geotechnical and regulatory challenges

Authors: Dohle, D Download Paper Open access courtesy of:

DOI https://doi.org/10.36487/ACG_repo/2615_90

Cite As:
Dohle, D 2026, 'Capping design for 2 tailings storage facilities with unique geotechnical and regulatory challenges', 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. 1-13, https://doi.org/10.36487/ACG_repo/2615_90



Abstract:
This paper describes the design and regulatory challenges encountered in the capping of 2 tailings storage facilities (TSFs) in Western Australia containing slightly radioactive tailings. The tailings has unique properties, comprising mostly clay-sized particles with a low plasticity index, high liquid and plastic limits, high void ratio and low dry density. The site is regulated under a landfill licence while dam safety guidance also applies. One of the key challenges of capping soft tailings is to provide safe and stable access for construction equipment. To estimate the tailings strength, existing cone penetrometer test (CPT) data, dynamic cone penetration (DCP) tests and vane shear tests (VST) were used. DCP tests and VSTs carried out at the same time and location yielded conflicting results. DCPs sank under self-weight, indicating very soft soil, while VSTs and test pits confirmed a soft to firm tailings strength. The potential mechanisms for this discrepancy are investigated. The sites are regulated under a landfill licence and require design of a geomembrane capping system to achieve maximum infiltration requirements. Given the tailings is highly compressible, over 3 m of settlement is expected. The final landform therefore had to be over-built to achieve a self-shedding surface after settlement. To reduce earthworks, the existing embankments were cut back for one site, requiring consideration of the existing freeboard requirements and geomembrane liner connection details. It is proposed that the required environmental freeboard no longer applies once the tailings is covered and the dam safety freeboards no longer apply once a design storm can be released in a controlled manner. The slight radioactivity of the tailings was accounted for by using a cap of sufficient thickness to delay the emission of radon until it has mostly decayed. The selected cap comprised general fill, a clay-rich subgrade, geomembrane and a revegetation layer.

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