Total existing and legacy oil sands fluid fine tailings (FFT) in Alberta exceeds 1.2 billion m3, posing an environmental challenge for both reclamation efforts and physical stability. Thickening of FFT by adding polymer flocculants is one of the cost-effective treatment technologies used by operators to dewater FFT to limit those volumes. This paper examines the effects of two new polymers (cationic and neutral) on the consolidation behavior of FFT compared to A3338 polymer treatment. Seven large strain consolidation experiments were completed; two for each polymer type and one control sample of untreated FFT. Sedimentation, filtration and basic properties of untreated FFT and FFT treatments were also analyzed.
Results indicate that the neutral polymer increased the initial hydraulic conductivity of FFT by four orders of magnitude compared to the cationic and anionic polymers. At the end of self-weight consolidation, a demonstrably higher dewatering efficiency of the neutral polymer on FFT was observed relative to the cationic and anionic polymers determined by calculating the net water release of each polymer. At each load step, the hydraulic conductivity and compressibility of FFT treated using the neutral and cationic polymers were higher compared to the anionic polymer. Moreover, above a solids content of 30 %, the neutral polymer produced about a 40 % increase in the shear strength of treated FFT relative to the cationic polymer, which is attributed to the distinct structure the neutral polymer creates following treatment. The measured capillary suction time of the samples immediately after treatment indicates that dewatering FFT by suction is seven times faster when FFT is treated using the cationic polymer than the anionic polymer.

Pilot studies of flocculated fluid fine tailings (fFFT) deposits are modelled using coupled large strain consolidation – creep formulations embedded in the UNSATCON software. The creep formulation employed is based on theory developed by Vermeer, a hypothesis B type model that implies a strain rate dependency on the location of the compressibility curve. The pilots comprised deposits of tailings placed in 14 m tall x 2.75 m wide caissons. Here we present comparisons of data from tailings flocculated with a conventional anionic polymer. Simulations are presented for large strain consolidation only, as well as creep-consolidation, using reasonable ranges in the k-e function and the creep parameters. The use of a creep model improves fits to all measured properties (settlement and depth profiles of density and pore-water pressure), compared to the consolidation only results, though agreement in still not perfect. Using different groups of plausible parameter sets, the model was then used to extrapolate to full scale behavior. In general, use of creep model results in relatively small (~10%) increase in the overall settlement of the deposits, but a marked decrease in the rate of pore-water pressure dissipation. The significance of these results to implantation for full scale deposits are discussed, as are areas of uncertainty requiring further attention.

A two-dimensional large strain consolidation model is presented. The model uses a piecewise linear formulation for large strain, which implies nodes that are associated with a constant mass of solids, whose positions are updated over time. Fluxes are calculated based on 2D gradients between adjacent nodes. Regions associated with each of these nodes to calculate fluxes only deform vertically, and can slip past each other. This appears to accommodate large strains without the need for remeshing due to mesh distortion, and appears to retain sufficient accuracy. The model is validated against other analytical and numerical solutions for axisymmetric and 2D consolidation. An example analysis of 2D consolidation in a hypothetical tailings impoundment is shown. The analysis shows the formation of a beach, and how the variable water height may affect overall consolidation.

Terrestrial reclamation of fluid fine tailing (FFT) containment ponds starts with a necessary dewatering process. The dewatered FFT in its dedicated disposal site is then expected to develop in to stable landscape by self-weight consolidation. The feasibility of the supposition was investigated using shear strength and consolidation measurements of thickened FFT; cake.
Shear strength measurements were conducted under inundated and drained conditions. The cake gave a linear Mohr-Coulomb failure envelope with 1.2kPa cohesive strength and 6⁰ friction angle. This indicates that the load bearing capacity of thickened FFT deposits is too low to support landscaping machinery.
The cake hydraulic conductivity was very low and similar to that of active clays. The coefficient of consolidation for the cake was nearly constant and had a mean value of 0.099 m2.s-1, also similar to active clays. The void ratio–effective stress–hydraulic conductivity power law relations constitutive constants were used as input to predict settlement using a finite-strain 1D model software. Model outputs indicate that consolidation by self-weight of cake, or thickened FFT deposit is extremely slow to create reclamation ready deposits. Both the shear strength and consolidation properties suggest that options that will increase the shear strength and hydraulic conductivity of thickened FFT have to be integrated in the process prior to placing them at final disposal sites. Amending the thickened FFT with coarse tailings can simultaneously increase the shear strength and hydraulic conductivity of thickened FFT and is likely the sole solution. The advantages of this method referred to as co-disposal thus far was not demonstrated because the coarse material was added into slurry (viscous) FFT, rather than thickened (plastic consistency) FFT reducing its impact. There are reports which raise the limitations of discharging treated FFT and this study goes farther by determining the geotechnical parameters.

The Alberta oil sands mining and extraction processes in Northern Alberta yield vast volumes of tailings which are mainly consisted of water, fine clay particles, sand, chemicals, and bitumen. The disposal of this mixture in the tailings pond is one of the main reasons causing gravity segregation to occur. During this process, the stable suspension also known as the fluid fine tailings (FFT), is formed, which requires many years to consolidate. Thus, land reclamation becomes a huge environmental issue. Therefore, a proper understanding of the transformation occurs in density and structuration of mine tailings may be important to better plan the operation of deposition in the tailings ponds such that reclamation can be done when these ponds are no longer in use. Thus, this paper reports on the initial results of an experimental program designed to monitor changes in density and structure in FFT using ultrasonic waves. The experiments include not only the evaluation of wave velocities (compressional and shear) but also the changes in wave attenuation as a function of time.