Authors: Seddon, KD; Dillon, MJ

Cite As:
Seddon, KD & Dillon, MJ 2009, 'The Effect of Evaporation on Strength and the Stability of Thickened Tailings Beach Slopes', in R Jewell, AB Fourie, S Barrera & J Wiertz (eds), Proceedings of the Twelfth International Seminar on Paste and Thickened Tailings, Australian Centre for Geomechanics, Perth, pp. 261-269.

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At the time a layer of tailings slurry comes to rest on the surface of a tailings beach and settles, it has very low shear strength. Before additional layers of tailings are placed over this layer, the strength must increase, or the driving forces of the accumulated tailings will exceed the shear strength, and mass instability will result. The undrained shear strength of tailings in a beach is a function of the moisture content and density of the tailings. Test methods to establish this relationship are discussed and compared. The effects of surface area and evaporative drying can be combined to analyse the final moisture content, density and shear strength achieved on a beach. The theoretical results are compared to the results of field trials. The influence of climate and tailings type can be important. Under critical combinations of climate, tailings and placement rate, very low strength layers may remain in the tailings at depth. In the first instance, a static type failure may result (i.e. a failure without any triggering mechanism such as an earthquake). A possible example of this type of failure is proposed.

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268 Paste 2009, Viña del Mar, Chile
Appendix: A note on units and terminology
In the context of this paper, the term “moisture content” is used to denote water content using the soil
mechanics convention of a dry weight basis. Moisture content (m) is usually expressed as a percentage, but
for convenience is used as a ratio in the equations presented in this paper, hence:
m = Mass water/Mass soil.
The concept of void ratio (e) is also used, as this has the advantage of eliminating differences that are
attributable to the soil particle density (G).
Void ratio is defined as Volume water/Volume solids, and:
m = e/G (N1)
The relationship between moisture content and the commonly used solids content (S) is:
m = (100 – s)/s
where s is a percentage.
Paste 2009, Viña del Mar, Chile 269

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