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Oil sands fluid fine tailings deposits are challenging to reclaim due to their inherently high natural water content, low permeability, and low strength. Combinations of polymers and (or) coagulants are used by operators to improve the dewatering and strength properties of the tailings. However, considerably more work has been done to evaluate polymer performance with short-term dewatering metrics rather than with long-term metrics such as consolidation properties. This paper evaluates the potential of four novel polymers for use in fluid fine tailings treatment compared to a commercially available polymer and untreated tailings specimen. The performance of the polymers was assessed through initial screening with respect to short-term dewatering, evaluation of the consolidation and strength properties using large-strain consolidation tests, shear sensitivity in pipeline transport, and finally, large-strain consolidation modelling to appraise the relative potential performance under different strategies, such as terrestrial or aquatic reclamation options. One polymer exhibits remarkably fast dewatering at high void ratios, while another demonstrates dense and shear-resistant flocs. The paper discusses each polymer's distinctive tailings fabrics and how their unique merits and limitations would benefit different reclamation eventualities. Finally, potential improvements of the polymers are suggested for future assessment. Key words: oil sands, tailings, polymers, consolidation, strength, modelling. Il est difficile de recuperer les depots de residus fins fluides de sables bitumineux en raison de leur teneur naturelle en eau elevee, de leur faible permeabilite et de leur faible resistance. Pour ameliorer les proprietes de deshydratation et de resistance des residus, les exploitants utilisent des combinaisons de polymeres et/ou de coagulants. Les performances des polymeres ont toutefois ete evaluees davantage en fonction de parametres de deshydratation a court terme qu'en fonction de parametres a long terme tels que les proprietes de consolidation. Le present document evalue le potentiel de quatre nouveaux polymeres pour une utilisation dans le traitement des residus fins fluides par rapport a un polymere offert sure le marche et a un echantillon de residus non traites. Les performances des polymeres ont ete evaluees par le biais d'une selection initiale concernant la deshydratation a court terme, revaluation des proprietes de consolidation et de resistance a l'aide d'essais de consolidation a grande deformation, la sensibilite au cisaillement dans le transport par pipeline et, enfin, la modelisation de la consolidation a grande deformation pour evaluer les performances potentielles relatives dans le cadre de differentes strategies, telles que les options de remise en etat terrestre ou aquatique. Les resultats montrent qu'un polymere presente une deshydratation remarquablement rapide a des taux de vide eleves, tandis qu'un autre presente des flocs denses et resistants au cisaillement. L'article aborde les materiaux de residus distinctifs de chaque polymere et la maniere dont leurs merites et limites uniques pourraient profiter a differentes eventualites de remise en etat. Enfin, des ameliorations potentielles des polymeres sont suggerees pour une evaluation future. [Traduit par la Redaction] Mots-cles: sables bitumineux, residus, polymeres, consolidation, resistance, modelisation., Introduction Surface mining of oil sands bitumen deposits produce tailings, which comprise water, sands, clays, residual hydrocarbons, and chemicals originating from the bitumen extraction process (Royal Society of Canada Expert [...]

New approaches are proposed for robustly determining the compressibility and permeability functions for large-strain consolidation (LSC), using limited measurements from one-dimensional tests, such as column or centrifuge experiments. These new methods are developed from several new findings reported in this paper, including (i) new analytical solutions that relate parameters of compressibility functions to the final density profile, (ii) analytical proof of the independence of the shape of the settlement curve from the parameter M, where the permeability or hydraulic conductivity k is given by MeP, e is void ratio, and M and P are material-related constants; and (iii) that when the same k function is employed, for the case of one-dimensional settlement, the optimal values of M and P are located on a unique straight line in the P-lnM space. The third finding was determined from optimization analysis of thousands of LSC simulations. Using different combinations of these new findings, three new methods are developed to estimate the permeability function. The efficiency, robustness, and accuracy of the three methods are investigated by their application to four column tests from the literature. The simplest of the three methods requires only two LSC analyses plus several hand-calculations, demonstrating strong potential for practical use. Key words: large-strain consolidation, deep learning, hydraulic conductivity. De nouvelles approches sont proposees pour determiner de facon robuste les fonctions de compressibility et de permeabilite pour la consolidation de grandes deformations (LSC), en utilisant des mesures limitees a partir d'essais unidimensionnels, tels que des experiences sur colonne ou centrifugeuse. Ces nouvelles methodes sont developpees a partir de plusieurs nouvelles decouvertes rapportees dans cet article, y compris (i) de nouvelles solutions analytiques qui relient les parametres des fonctions de compressibilite au profil de densite final, (ii) la preuve analytique de l'independance de la forme de la courbe de tassement du parametre M, ou la permeabilite ou conductivite hydraulique k est donnee par MeP ou e est l'indice des vides et M et P sont des constantes liees au materiau; et (iii) que lorsque la meme fonction k est utilisee, dans le cas du tassement unidimensionel, les valeurs optimales de M et P sont situees sur une droite unique dans l'espace P-lnM. Le troisieme resultat a ete determine a partir de l'analyse d'optimisation de milliers de simulations LSC. En utilisant differentes combinaisons de ces nouvelles decouvertes, trois nouvelles methodes sont mises au point pour estimer la fonction de permeabilite. L'efficacite, la robustesse et l'exactitude des trois methodes sont etudiees en les appliquant a des tests a quatre colonnes tires de la litterature. La plus simple des trois methodes ne necessite que deux analyses LSC et plusieurs calculs manuels, ce qui demontre un fort potentiel d'utilisation pratique. [Traduit par la Redaction] Mots-cles: consolidation de grandes deformations, apprentissage en profondeur, conductivite hydraulique., Introduction Fine-grained materials are deposited in various geotechnical industrial activities, such as deposition of dredged sludges in or near water bodies (Palermo et al. 2008); in estuaries and offshore for [...]

Tailings may undergo desiccation stress history under varied climatic and depositional parameters. While tailings substantially dewatered prior to deposition may experience desiccation under the greatest range of climatic variation, even conventionally deposited tailings may desiccate in arid climates at lower rates of rise. Bench-scale research has shown that the stress history imparted by desiccation substantially improves strength in gold tailings. The present study further investigates this phenomenon by simulating multi-layer deposition of high-density tailings using a modular drying box, 0.7 m by 1 min plan. The box is instrumented for directly measuring evaporation, drainage, water content, vertical volume change, and matric suction. Additional measurements included total suction at the surface as well as observations of crack development. The dewatering behaviour conforms to that predicted by previously published generic modelling, specifically that the presence of partially desiccated tailings initially accelerates, but then decelerates dewatering of fresh tailings. The shear behaviour of samples obtained using buried tubes and by driving thin-wall tubes into the multi-layer simulation are compared with shear behaviour of samples from bench-scale experiments. Shear strength of samples from the multi-layer simulation is independent of the sampling method, and shows higher strength than the bench-scale samples. The higher strength may be due to the greater number of wet-dry cycles or other age-related processes. Key words: tailings, desiccation, drying box, simple shear, cyclic. Les refus peuvent subir une etude des contraintes deja subies de dessiccation sous des parametres climatiques et sedimentaires varies. Malgre que des residus deshydrates en grande partie avant le depot peuvent eprouver la dessiccation sous la plus grande portee de variations climatiques, meme les residus conventionnellement deposes peuvent se dessecher dans les climats arides a des taux inferieurs d'elevation. Des recherches a l'echelle de banc d'essai ont montre que l'etude des contraintes deja subie conferee par la dessiccation ameliore considerablement la resistance dans les residus d'or. La presente etude examine davantage ce phenomene en simulant des depots de residus a multicouche a haute densite a l'aide d'une boite de sechage modulaire, 0,7 m par 1 m en plan. La boite est instrumentee pour mesurer directement l'evaporation, le drainage, la teneur en eau, le changement de volume vertical et la succion matricielle. Des mesures supplementaires inclus la succion totale a la surface et des observations du developpement de la fissure. Le comportement de deshydratation est conforme a celle predite par la modelisation generique deja publiee, plus precisement que la presence de residus desseches partiellement accelere initialement, mais puis ralentit la deshydratation des residus frais. Le comportement en cisaillement d'echantillons obtenus a l'aide de tubes enterres, en enfoncant des tubes a paroi mince dans la simulation a multicouche, est compare avec le comportement en cisaillement des experimentations a l'echelle de banc d'essai. La resistance au cisaillement des echantillons de la simulation a multicouches est independante de la methode d'echantillonnage, et montre une plus grande resistance que les echantillons a l'echelle de banc d'essai. La resistance la plus elevee peut etre a cause du plus grand nombre de cycles de mouillage- sechage ou d'autres processus lies a l'age. [Traduit par la Redaction] Mots-cles: residus, dessiccation, boite de sechage, cisaillement simple, cyclique., Introduction In the last few decades, more than 50 tailings impoundments have failed due to seismic activity, liquefaction, foundation failure, etc. Many of these failures have been attributed to liquefaction [...]

Hydration occurring in cemented paste backfill (CPB) is shown to generate matric suction through selfdesiccation. This complicates determination of the water-retention curve and mechanical properties during curing, which are important in stope design, and renders problematic the use of axis-translation testing procedure to control suctions in strength testing. An alternative is to monitor suction directly during testing. To this end, a miniature tensiometer is inserted into the base of a triaxial cell. A series of unconfined and confined tests are performed on early-age (less than two weeks old) CPB. The observed behaviour is similar to that observed in weakly cemented soils, showing a distinct tendency to dilate during shearing. Key words: cemented paste backfill, matric suction, unsaturated soil, cemented soil, triaxial testing. On a montre que l'hydratation qui se produit dans les remblais de pate de ciment <> genere une succion matricielle par auto-dessiccation. Ceci complique la determination de la courbe de retention d'eau et des proprietes mecaniques durant le murissage, qui sont importantes dans la conception de gradins, et rend problematique l'utilisation de la procedure d'essais par translation d'axe pour controler les succions dans les essais de resistance. Une alternative consiste a mesurer la succion directement durant l'essai. A cette fin, un tensiometre miniature est insere dans la base de la cellule triaxiale. Une serie d'essais confines et non confines sont realises tot dans l'histoire de la pate <> (moins de deux semaines). Le comportement observe est similaire a celui observe dans les sols faiblement cimentes, montrant une tendance distincte a se dilater durant le cisaillement. Mots-cles : remblai de pate cimentee, matrice de succion, sol non sature, sol cimente, essais triaxiaux., [Traduit par la Redaction] Introduction Cemented paste backfill (CPB) is a mixture of tailings, water, and cement used to fill underground mined-out stopes. The use of backfill reduces the amount [...]

The soil--water characteristic curve (SWCC) of fine-grained soils is usually determined experimentally. In the design of mine waste covers and landfill liners, the unsaturated hydraulic conductivity function, k(h), is often derived theoretically from the measured SWCC. Implicit in these derivations is the transformation of the SWCC to a pore-size distribution (PSD), typically assumed to be constant and monomodal. However, PSD measurements of a clayey till compacted at various water contents after compaction, after flexible-wall permeability testing and before and after SWCC tests show that the PSD of the same material varies significantly under the stated physical conditions. Predictions of the SWCCs using PSDs measured both before and after the SWCC tests significantly underpredicted the values measured. By applying a simple transformation to the PSD to account for the scaling effect from the porosimetry samples (approximately 1 g dry weight) to the SWCC test samples (approximately 200 g dry weight), the predicted SWCCs were found to envelop the measured values. A simple model that simulates the change in PSD during the SWCC test predicted water contents close (1% root mean square error) to the measured SWCCs. CE Database subject headings: Landfills; Mine waste; Soil water; Hydraulic conductivity; Pore size distribution; Liners.

A piecewise-linear formulation for simulating coupled large-strain consolidation and unsaturated flow using a mass-conservative and noniterative solution was developed in a companion paper and implemented in a proposed program called UNSAT-CON. The formulation is tested in this paper using numerical cases as well as laboratory and field data. First, UNSAT-CON is tested by comparing model predictions to published predictions of a finite-element-based model that uses a quasi-unsaturated formulation to model evaporation: the same quasi-unsaturated formulation is implemented in UNSAT-CON to allow direct comparison. Excellent agreement of settlement over time for various levels of evaporation are obtained. UNSAT-CON reliably predicts the hydraulic exchange at the soil-atmosphere interface under the conditions of evaporation, decantation, or their combinations. The fully unsaturated formulation is tested on fine-grained tailings by calibration with a documented laboratory column test and verification with a 4.1-m-deep field trial. This testing exercise showed (1) threedimensional (3D) constitutive surfaces are largely constrained when defined using conventional test data such as the saturated compressibility function and soil water characteristic curve; (2) good to excellent agreement between measurements and predictions are observed, including the developing suction, decreasing void ratio, increasing solid content, and increasing settlement rate due to evaporation effect on the near surface zone; and (3) modeling desaturation allows for a more-realistic simulation of deformation in the unsaturated zone than using formulations that do not model desaturation. [ABSTRACT FROM AUTHOR]

A mass-conservative formulation of one-dimensional (1D) coupled large-strain consolidation and unsaturated flow using a piecewise-linear formulation is developed. The volume and water-content changes in the unsaturated zone are described using threedimensional (3D) constitutive surfaces of void ratio and gravimetric water content as functions of net stress and matric suction, whereas the volume change in the saturated zone is described using a two-dimensional (2D) curve relating void ratio to Terzaghi effective stress. The hydraulic conductivity varies with both void ratio and suction in the unsaturated zone, and with void ratio only in the saturated zone. The associated nonlinearities are addressed by solving the flow-continuity equation for water mass conservation through a finite-difference scheme in a piecewise-linear manner. The unknowns are calculated from variables in the previous time step without requiring iteration. A novel algorithm is developed to smoothly model transition between the saturated and unsaturated zones. Four types of top boundary conditions are formulated to account for complex soil-atmosphere hydraulic interactions. The developed program is also capable of performing a quasi-unsaturated analysis, which uses the saturated soil's constitutive relationships in the unsaturated zone, similar to the approach of several models currently used in practice. The theoretical and numerical development of the model is described in this paper, and is followed by verifications of the program's implementation using a numerical example of saturated large-strain consolidation and an analytical solution to unsaturated flow. Validation of the quasi-unsaturated and unsaturated formulations is presented in the companion paper, using comparisons with numerical cases as well as laboratory and field data. [ABSTRACT FROM AUTHOR]