Effect of mine waste rock inclusions on the consolidation of tailing

E.M. Jaouhar, Michel Aubertin, M. James

Dans les comptes rendus d’articles de la conférence: GEO2011: 64th Canadian Geotechnical Conference, 14th Pan-American Conference on Soil Mechanics and Geotechnical Engineering, 5th Pan-American Conference on Teaching and Learning of Geotechnical Engineering

Session: Geoenvironmental Engineering

ABSTRACT: Mining of hard rock ore deposits produces granular, cohesionless tailings with a grain size distribution dominated by the silty fraction. The deposition of these tailings as slurry induces a loose state, with high pore-water pressures and low resistance to static and cyclic loadings. Due to the high fines content, the self-weight consolidation of these deposits is a long process. This process can be accelerated through the use of pervious inclusions. This paper presents the results of a numerical investigation of the use of drainage inclusions made of waste rock. These waste rock inclusions, which are much more pervious than the surrounding tailings, facilitate dissipation of the pore-water pressures induced during deposition and thus accelerate consolidation. Results of finite element simulations are presented to illustrate the effects of these inclusions on pore-water pressure dissipation. Additional simulations were conducted to assess the influence of various factors on the response of tailings.

RÉSUMÉ: miniers en roches dures produit des résidus de faible cohésion ayant une granulométrie dominée par la fraction silteuse. Le transport hydraulique et le dépôt de ces résidus induisent un état lâche, avec des pressions interstitielles élevées et une faible résistance aux chargements statique et cyclique. La consolidation naturelle des résidus sous leur propre poids est un long processus. Cette phase peut être accélérée en utilisant des inclusions drainantes. ne étude numérique formées de roches stériles pour accélérer la consolidation des résidus miniers. Ces inclusions de roches stériles, qui sont beaucoup plus perméables que les résidus, aident à dissiper la pression interstitielle en excès pendant le remplissage du bassin. Les D'autres simulations sont également menées pour évaluer l'influence de divers facteurs sur la réponse des résidus 1. INTRODUCTION There have been several failures of tailings impoundments over the last few decades. The associated flow of liquefied material has resulted in loss of life as well as environmental and economic damage. The risk of failure can be reduced by applying a co-disposal technique consisting of placing waste rock inclusions (WRI) within an impoundment, prior to and during tailings deposition, as shown on Figure 1 (Aubertin et al. 2002; James and Aubertin 2009, 2010). The waste rock is used to create continuous inclusions (internal dykes) or isolated heaps within the impoundment to provide additional drainage to accelerate consolidation and reinforcement, thus increasing the stability of the tailings. Some of the potential benefits of this method have been confirmed by laboratory tests on a seismic simulator (Pépin et al. 2009) and by numerical simulations of tailings impoundments with and without WRI under cyclic loadings (James 2009). This paper presents a numerical modeling investigation of the use of waste rock inclusions to accelerate the consolidation of slurry-deposited tailings through the dissipation of pore-water pressures (PWP). An objective of this study was to assess some of the factors that influence the dissipation of PWP in the impoundment during tailings deposition. Figure 1: Schematic illustration of a tailings impoundment with waste rock inclusions placed prior to and during tailings deposition (Adapted from James and Aubertin 2010).

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