12.10 Methods of Tailings Disposal
The use of tailings material is generally the most economical construction method. As discussed previously, some of the disadvantages of using tailings as dam-building material include high susceptibility to internal piping, highly erodible surfaces, and high susceptibility of the fine tailings to frost action. Also, loose and saturated tailings are subjected to liquefaction under earthquake shocks. Sand fractions, after being separated from the slimes, may be easy to compact using vibratory compactors to obtain a dense mass of strong material that has greatly increased resistance to liquefaction. The three methods of construction using tailings are upstream, downstream and centerline.
Raised embankments can be constructed using upstream, downstream, or centerline methods (figure 7). Each of the structures, for instance, is constructed in four successive lifts with constructing material and the fill capacity increases incrementally with each successive lift. They have a lower initial capital cost than retention dams, because fill material and placement costs are phased over the whole life of the impoundment. The choice available for construction material are increased because of the smaller quantity needed at any one time. Retention dams generally use natural soil, whereas raised embankments can use natural soil, tailings, and waste rock in any combination.
Figure 7. Embankment Types: (a) Upstream, (b) Centerline, (c) Downstream or Water Retention
Figure 8: Water-Retention type Dam for Tailings Disposal