Geotechnical Stability of Tailings Dams
Symposium Rouyn-Noranda 2002
Darcy Jolette, Micheal James, Olivier Riffon, Bruno Bussière,
Mill tailings are usually transported to a surface impoundment area as slurry. The main environmental problems concerning tailings ponds where mill tailings are stored are: i) physical stability of the retaining dams and ii) chemical stability of the tailings. The geotechnical stability problems encountered with mill tailings can generally be linked to the material in place, which is loose and highly saturated (at least in certain areas of the pond). These tailings consolidate slowly due to their placement method, their water content and their low hydraulic conductivity.
The stability of tailings retaining dams can be compromised by various specific problems. The aspects discussed in this presentation include the risks associated with: submersion of the crest by rise of excess water in the pond, the retrogressive erosion of the dam and foundation material caused by too high water pressures, surface erosion due to water entrainment of particles, sliding of unstable zones along the slope due to static and dynamic loads, liquefaction potential due to dynamic loads and the strength of the foundation material regarding settling and failure. Catchment dams must be well designed to support the various combinations of loads in anticipated worst-case scenarios. With this in mind, we will discuss the choice of the safety factor as a function of the nature of the works, the type of failure anticipated, the type of load considered and the probability of a critical event taking place. Certain techniques that could help improve the mechanical and hydraulic properties of the tailings placed in the tailings ponds will also be discussed during the presentation.