McKenna, G 2023, 'How to compact filtered tailings', in GW Wilson, NA Beier, DC Sego, AB Fourie & D Reid (eds), Paste 2023: 25th International Conference on Paste, Thickened and Filtered Tailings
, University of Alberta, Edmonton, and Australian Centre for Geomechanics, Perth, pp. 440-454, https://doi.org/10.36487/ACG_repo/2355_33
To control the risk of static or dynamic liquefaction, filtered tailings stacks are typically designed to be compacted and to remain unsaturated. In theory, compacting filtered tailings should be easy, since mines tend to produce a consistent, well-graded sandy silt or silty sand tailings. The filter presses are designed to produce tailings with a geotechnical moisture content within a narrow range; modest-sized equipment can compact the tailings in thin lifts; and traditional earthworks quality control methods are common and readily available.
In practice, however, filtered tailings and mine owners often discover that the learning curve associated with compacting filtered tailings can be steeper than expected.
The filter plant will typically produce tailings that are somewhat wet of the standard Proctor optimum moisture content, making compaction difficult. If not protected, tailings at the loadout can absorb water or freeze. The tailings stack must be kept graded to promote runoff. In some climates, evaporation may be insufficient for drying; in others, snow, ice, and freezing conditions present a challenge. At some mines, the tailings liquefy under cyclic loading by dozers, trucks, or compactors as they are being placed.
Choosing a tailings field-density specification is not straightforward, especially where high stresses at the base of the stack can increase the risk of static or dynamic liquefaction. Method specs for compaction may be employed, but can be unreliable under certain conditions. A nuclear densometer often does not provide accurate readings of the density of some tailings, particularly those with elevated levels of metals.
This paper presents practical, hard-won lessons and solutions from the field to aid in the design, operation, and closure of filtered tailings facilities based on firsthand experience in Canada and interviews with operators around the world, lessons that can help shorten the learning curve for new and existing filter stack operations.
Keywords: compaction, filtered tailings, earthworks, geotechnical, landform design, density, liquefaction, moisture, tailings stack, quality assurance, quality control.
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