Effective Stress Analyses to Assess the Stability of Progressively Raised Upstream Dikes for Tailings Impoundments with Waste Rock Inclusions

The design of retaining dikes for tailings deposited hydraulically in surface impoundments raises various geotechnical issues, including the risk of instability along the external slope. Coarse grained waste rock produced at the mine can be placed within the impoundment to create stiff and draining inclusions that greatly improve stability by accelerating consolidation and providing reinforcement. This paper presents results from stability analyses conducted to assess the effect of WRI on the static stability of reinforced tailings impoundments with progressively raised upstream dikes, considering different geometries and loading conditions. Emphasis of these analyses is placed on effective stress calculations that take into account the generation and dissipation of excess porewater pressures induced by sequential deposition of tailings layers, which leads to transient increases of the excess porewater pressures and reduction of the factor of safety. The stability calculations results, obtained from a combination of transient finite element and limit equilibrium analyses, show the positive influence of adding WRI on critical short term response, and illustrate how such inclusions can be used to enhance the stability of retaining dikes.