Analysis of Tailings Dam-Break and Run-Out

The designers of surface tailings dams are routinely required to carry out dam-break and run-out analyses, which have become more important with the ongoing failure of tailings dams worldwide. The analysis methods conventionally used are based on the more simple analysis of water dam-break and run-out. However, tailings dams add the complexities that tailings, being viscous, resist flow, and an unknown proportion of the tailings are released, rather than the full loss of water on water dam-break. As a result, the analysis tools developed for assessing the potential for tailings dam failure are more difficult to use and less reliable than those used for water dams, and are necessarily semi-empirical. The modeling of large-scale dam-break and run-out processes may be classified numerically as a large-strain deformation problem, making them very complex and difficult to solve. Popular modeling methods include the discrete element method (DEM), smoothed particle hydrodynamics (SPH), and the material point method (MPM). In the DEM, each particle is considered discretely; hence, the macroscopic behavior cannot practically be modelled directly. On the other hand, the SPH and MPM are derived from continuum mechanics, which allows the use of conventional geotechnical constitutive models. A run-out analysis using the MPM has been applied to simulate the reported run-out from the Mount Polley tailings dam failure, and the results obtained are seen to match reasonably well the reported progressive failure of the dam and the extent of the run-out. Despite the limitations that a numerical simulation may present, the use of numerical techniques is invaluable in understanding the kinematics of a tailings dam-break and run-out. It can provide information for use in risk assessments, such as the delineation of the area that would potentially be affected by the run-out, and the quantification of potential losses of human life, infrastructure, and environmental assets. The delineation of the extent of a potential run-out from a tailings dam failure can also enable planning for the safe evacuation of downstream inhabitants and rapid recovery post-failure.