Determination of field-representative consolidation properties of oil sands fine tailings by back-analysis of instrumented deposition trials

Srboljub Masala, Reza Nik, Gavin Freeman, Robert Mahood

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

Session: Mining Geotechnics

ABSTRACT: ion of field-representative consolidation properties of oil sands fine tailings by back-analysis of instrumented deposition trials Srboljub Masala Barr Engineering and Environmental Science Canada, Calgary, Alberta, Canada Reza Nik, Gavin Freeman & Robert Mahood Shell Canada Energy, Calgary, Alberta, Canada ABSTRACT Material properties for consolidation analyses of soft oil sands tailings deposits are usually directly determined by laboratory tests on tailings slurry. However, it is well known that, with a laboratory determined input for consolidation analyses, the predictions do not match the observed settling behavior at larger scales, typically significantly underestimating it. This discrepancy arises due to differences of the soil structure of tailings deposited in a pilot test cell or a commercial pond and the soil structure of the laboratory specimen of the same material. This results in different material properties that characterize the two settling processes. A solution to this problem is to derive input parameters for consolidation analyses by back-analyzing monitoring data of instrumented pilot-scale deposition trials or commercial-level operations. The paper presents the methodology that was successfully used for the interpretation of two deposition trials with thickened tailings at Shell Ca. RÉSUMÉ de la consolidation pour les propriétés des matériaux pour dépôt de résidus de sables bitumineux sont généralement déterminées par des essais dans laboratoire sur les boues (résidus en suspension). Il est bien connu que les données déterminés dans le laboratoire pour l'analyse de la consolidation ne correspondent pas au comportement observé à plus grandes échelles, à cause de la différence entre la structure du sol de résidus déposés dans une cellule de test pilote ou d'un bassin commercial et la structure du sol des échantillons de laboratoire de la même matière. Une solut des données de sauvegarde des essais de dépôt à l'échelle pilote ou des opérations au niveau commercial pour l'analyse de la consolidation. Ce document présente la méthodologie qui a été utilisée avec succès pour l'interprétation de deux essais de dépôt des résidus épaissis à Shell Canada Tailings Testing Facility. 1 INTRODUCTION 1.1 marked the beginning of soil mechanics as an engineering discipline. Key assumptions of this theory were that the soil is homogeneous and saturated, the soil components are incompressible, the strains are small (soil sample or deposit is thin), the self-weight can be neglected, the relationship between void ratio and effective stress is linear, body forces are neglected, and the permeability does not change during consolidation process (Terzaghi and Peck, 1978). The theory was limited to one-dimensional conditions as it was developed for determination of settlements caused by loads from buildings or embankments as common soil mechanics problems. A problem of back-calculation of the coefficient of consolidation cv, the governing parameter theory, from oedometer or field data came into focus early after adoption of the theory in the engineering practice. The solutions provided by Casagrande and Taylor in the and soil mechanics textbook. The coefficient of consolidation is a function of the applied vertical stress, but the analyses typically assume it remains constant. The coefficient of consolidation depends on the compressibility, permeability and initial void ratio of a soil. Subsequent evolution of both the theory and the methods for determination of its governing parameter(s) derivation, by introducing additional complexities through removal of - some of original simplifying assumptions - as non-representative of the real conditions. the needs of the mining industry and large civil engineering infrastructural projects, which required prediction of settlements and consolidation rates in unusual conditions of very soft ground or fill material, at temporal and spatial scales very different from traditional geotechnical projects. The consolidation processes in deep tailings basins or over extensive areas of reclaimed soft ground were directly deformations were not small, body forces (self-weight) were much larger than applied loads, material properties exhibited significant changes during deformation process, etc. theory typically leads to an underestimation of the magnitude and an overestimation of the degree of consolidation.

RÉSUMÉ: mination of field-representative consolidation properties of oil sands fine tailings by back-analysis of instrumented deposition trials Srboljub Masala Barr Engineering and Environmental Science Canada, Calgary, Alberta, Canada Reza Nik, Gavin Freeman & Robert Mahood Shell Canada Energy, Calgary, Alberta, Canada ABSTRACT Material properties for consolidation analyses of soft oil sands tailings deposits are usually directly determined by laboratory tests on tailings slurry. However, it is well known that, with a laboratory determined input for consolidation analyses, the predictions do not match the observed settling behavior at larger scales, typically significantly underestimating it. This discrepancy arises due to differences of the soil structure of tailings deposited in a pilot test cell or a commercial pond and the soil structure of the laboratory specimen of the same material. This results in different material properties that characterize the two settling processes. A solution to this problem is to derive input parameters for consolidation analyses by back-analyzing monitoring data of instrumented pilot-scale deposition trials or commercial-level operations. The paper presents the methodology that was successfully used for the interpretation of two deposition trials with thickened tailings at Shell Ca

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Srboljub Masala; Reza Nik; Gavin Freeman; Robert Mahood (2014) Determination of field-representative consolidation properties of oil sands fine tailings by back-analysis of instrumented deposition trials in GEO2014. Ottawa, Ontario: Canadian Geotechnical Society.

@article{GeoRegina14Paper303,author = Srboljub Masala; Reza Nik; Gavin Freeman; Robert Mahood,title = Determination of field-representative consolidation properties of oil sands fine tailings by back-analysis of instrumented deposition trials ,year = 2014}