The new GeoREF geotechnical beam centrifuge: modeling tailings consolidation

G. Zambrano-Narváez, J.D. Scott, R.J. Chalaturnyk

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

Session: Laboratory and Field Testing

ABSTRACT: oREF geotechnical beam centrifuge: modeling tailings consolidation G. Zambrano-Narváez, J. D. Scott and R.J. Chalaturnyk Department of Civil & Environmental Engineering, University of Alberta, Edmonton, AB, Canada ABSTRACT A new 2 m radius platform 50 g-tonne beam centrifuge, the first of its kind in Western Canada, with a maximum acceleration level of 280 rpm (150 g) and maximum payload of 500 kg has been installed as part of a multimillion dollar investment in a Geomechanical Reservoir Experimental Facility (GeoREF) at the University of Alberta. Geotechnical beam centrifuge tests are used to verify or improve mathematical models in predicting the change in volume behaviour of tailings. The objectives of the centrifuge tests were to evaluate the sedimentation/self weight consolidation behaviour of oil sand tailings using the centrifuge at the stress levels corresponding to the stresses in a tailings pond and to generate long term experimental data for numerical model verification. The paper describes the properties of the oil sands fluid fine tailings which hinder the analyses of centrifuge tests. As well the centrifuge machine, data acquisition system and initial results of centrifuge tests on oil sands fluid fine tailings are presented. RÉSUMÉ Un nouveau 2 m de rayon centrifugeuse plate-forme de 50 faisceau g-tonne, la première de son genre dans l'Ouest canadien , avec un niveau d'accélération maximale de 280 tours par minute (150 g) et une charge utile maximale de 500 kg a été installé dans le cadre d'un investissement de plusieurs millions de dollars dans un établissement Géomécanique du Réservoir Expérimental (GeoREF) à l'Université de l'Alberta . Essais de centrifugeuses à faisceau géotechniques sont utilisés pour vérifier ou améliorer les modèles mathématiques pour prédire le changement de comportement de volume de résidus. Les objectifs des essais de centrifugeuses étaient d'évaluer le comportement de consolidation sédimentation / auto de poids de résidus de sables bitumineux à l'aide de la centrifugeuse les niveaux de stress correspondant à des contraintes dans un bassin de résidus et de générer des données expérimentales à long terme pour la vérification de modèle numérique. Le document décrit les propriétés des sables bitumineux résidus fins fluides qui entravent les analyses des essais de centrifugeuses. Ainsi la machine de centrifugation, système d'acquisition de données et les premiers résultats des tests de centrifugation sur sables bitumineux résidus fins fluides sont présentés. 1 INTRODUCTION The total area covered by oil sands tailings ponds in 2010 was 176 km² and as 200 million litres per day continues to be accumulated in the five active mines, the area is forecast to increase to 250 km² by 2020. This has led to the accumulation of 900 million m³ of fluid fine tailings which require long-term storage in tailings ponds as the water is toxic and cannot be released. The reason for this massive accumulation is that the fluid fine tailings consolidate extremely slowly. Extensive research is underway by a number of organizations to develop methods to understand the reasons for this slow consolidation and to design treatment methods for the fluid fine tailings. Large strain consolidation tests are used to determine the consolidation properties of the fine tailings but because the fine tailings have such a large void ratio and the permeability is so low, these tests take over 5 months to perform. The slow dewatering behaviour and the dissimilarity between stresses in conventional test cells and field tailings ponds necessitates the use of a centrifuge for evaluating the self-weight sedimentation/consolidation of oil sands fluid fine tailings. A new geotechnical centrifuge in the Geomechanical Reservoir Experimental Facility (GeoREF) at the University of Alberta has been developed to model tailings consolidation and the experimental equipment and initial tests on oil sands fluid fine tailings are discussed. Several properties of the fluid fine tailings make the interpretation of centrifuge tests difficult; they are overconsolidated from thixotropy, the hydraulic conductivity can vary with hydraulic gradient and the gap-graded particle size distribution may result in segregation. Field volume change of the fluid fine tailings was modeled in a 10 m high standpipe test. Much of the settlement of the tailings was by creep not consolidation as it took place without a significant increase in effective stress (Scott et al, 2013). As creep effects cannot be determined in centrifuge tests, this effect also must be considered when analyzing centrifuge test results. 2 GEOTECHNICAL PROPERTIES OF THE FLUID FINE TALINGS Although the properties of the oil sands ore changes over the 30,000 km² oil sands mining area, the tailings properties are more affected by the bitumen extraction process and by the addition of various chemical additives to enhance the extraction process and tailings disposal processes. Typical tailings streams contain from 80% to 90% sand (>45 µm) but, because of the poorly graded particle distribution of the tailings and a large void ratio, on disposal in a tailings pond much of the sand settles out rapidly to form dykes and beaches and the remaining

RÉSUMÉ: ew GeoREF geotechnical beam centrifuge:

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Cite this article:
G. Zambrano-Narváez; J.D. Scott; R.J. Chalaturnyk (2014) The new GeoREF geotechnical beam centrifuge: modeling tailings consolidation in GEO2014. Ottawa, Ontario: Canadian Geotechnical Society.

@article{GeoRegina14Paper230,author = G. Zambrano-Narváez; J.D. Scott; R.J. Chalaturnyk,title = The new GeoREF geotechnical beam centrifuge: modeling tailings consolidation ,year = 2014}