Numerical modeling of multi-lift thickened tailings, considering the effects of evaporation

M.D. Fredlund, L. Xu, A. Hammami

In the proceedings of: GeoRegina 2014: 67th Canadian Geotechnical Conference

Session: Mining Geotechnics

ABSTRACT: This paper focuses on the numerical modelling of the complex process of thickened tailings deposition in thin lifts. Previous attempts to model this deposition have focused only on modelling the large-strain consolidation aspects of the problem. In the thin-lift deposition of thickened tailings a significant portion of the dewatering relies on evaporation. Accounting for such evaporation in the numerical modelling process is crucial to adequately represent reality. This paper is focused on one particular study using a single material property and a single average climate scenario to determine the potential differences between a standard large-strain consolidation numerical model and a numerical model which also considers the additional effects of i) unsaturated flow, and ii) actual evaporation (AE). The formulation for unsaturated flow consistent with the existing unsaturated flow formulation is integrated with this approach. Recent research utilizing the combined Fredlund-Wilson-Penman climatic calculation of actual evaporation from the surface of the tailings will also be considered in the formulation. The intent is to improve the ability of a software solution to accurately calculate evaporation from the material surface and therefore update the calculations of large-strain consolidation accordingly. Climatic data utilized for this study will be averaged based on site data collected for the site over the previous decades. RÉSUMÉ Cet article se concentre sur la modélisation numérique du processus complexe de épaissie dépôt des résidus dans les ascenseurs minces. Les tentatives précédentes pour modéliser ce dépôt ont porté uniquement sur la modélisation des aspects consolidation grand de contrainte du problème. Dans le dépôt mince ascenseur de résidus épaissis une partie importante de la déshydratation repose sur l'évaporation. Comptabilisation d'une telle évaporation dans le processus de modélisation numérique est crucial de représenter adéquatement la réalité. Ce document est axé sur une étude particulière en utilisant une propriété de la matière et un seul scénario climatique moyenne pour déterminer les différences de potentiel entre une consolidation modèle numérique standard très souche et un modèle numérique qui tient également compte des effets supplémentaires de i) d'écoulement insaturé, et ii) l'évaporation réelle (AE). La formulation pour l'écoulement insaturé compatible avec la formulation d'écoulement insaturé existant est intégré à cette approche. Des recherches récentes utilisant la Fredlund-Wilson-Penman calcul climatique combiné de l'évaporation réelle de la surface des résidus sera également prise en compte dans la formulation. Le but est d'améliorer la capacité d'une solution logicielle pour calculer avec précision l'évaporation à partir de la surface du matériau et par conséquent de mettre à jour les calculs de consolidation à grande déformation en conséquence. Les données climatiques utilisées pour cette étude seront en moyenne sur la base de données du site recueillies pour le site au cours des décennies précédentes. 1 INTRODUCTION Tailings are a by-product of mining industries, and are usually disposed of in above-ground impoundments. They undergo a complex process of sedimentation, consolidation under their self-weight, and evaporation over time (Seneviratne et al., 1996). Because of low permeability of tailings, the consolidation process may continue for several years after disposal has ceased. This may create delays in the ultimate dewatering and closure of tailings facilities. Therefore, proper management technologies are required for the disposal of tailings. One such approach being considered is disposing of the tailings in thin layers and exposing each layer to evaporation, so that a higher rate of dewatering of the tailings may be obtained. Physical modelling or field tests would make enormous demands on time and resources. Numerical models have potential advantages in both planning and strategic operations, as well as for parametric studies. This paper presents the results of one-dimensional (1D) numerical modelling of a specific multi-lift scenario. The purpose of the study is to gain a further understanding of the performance of thin layers of thickened tailings placed in the field. It is assumed that the thin placement of layers will optimise the influence of evaporation on the drying process and increase shear strength. The numerical simulations are conducted using the SVFlux/SVSolid (SoilVision Systems, 2012) software, which couples large-strain consolidation as well as a climatic numerical model to determine the influence of climate on the multi thin-layer placement of thickened tailings in a multi-year scenario. The results after one, three, and 14 years of tailings deposition will be presented. The 14-year scenario is broken into nine years of deposition followed by a two-year long quiescent period

RÉSUMÉ: ical modeling of multi-lift thickened tailings, considering the effects of evaporation

Access this article:
Canadian Geotechnical Society members can access to this article, along with all other Canadian Geotechnical Conference proceedings, in the Member Area. Conference proceedings are also available in many libraries.

Cite this article:
M.D. Fredlund; L. Xu; A. Hammami (2014) Numerical modeling of multi-lift thickened tailings, considering the effects of evaporation in GEO2014. Ottawa, Ontario: Canadian Geotechnical Society.

@article{GeoRegina14Paper295,author = M.D. Fredlund; L. Xu; A. Hammami,title = Numerical modeling of multi-lift thickened tailings, considering the effects of evaporation,year = 2014}