CONSOLIDATION BEHAVIOUR OF COKE-CAPPED
OIL SAND FLUID FINE TAILINGS
Maki Ito & Shahid Azam
Faculty of Engineering and Applied Science, University of Regina, Regina, Saskatchewan, Canada
ABSTRACT
The large volume and the slow consolidation of fluid fine tailings (FFT) pose serious challenges to contain the
environmental footprint of the oil sand industry. Several pre-depositional approaches, such as thickening, centrifugation,
and composite tailings production, have been used to accelerate slurry dewatering. Further improvement through postdepositional consolidation of the modified tailings stream can be achieved through external loads. Petroleum coke (a
carbon-based solid derived from bitumen refining) is a good candidate for this purpose because it is non-sinking (specific
gravity of 1.5) when applied on FFT surface in a tailings containment facility. The main purpose of this paper is to
understand the consolidation behaviour of FFT capped with coke. A quiescent one-dimensional large-strain consolidation
model was developed by employing the governing equation formulated in terms of excess pore water pressure and using
the FlexPDE software. The typical constitutive relationships of void ratio versus effective stress and void ratio versus
hydraulic conductivity were used to obtain the fit parameters for FFT. Various heights of coke layers were imposed on
the top surface of a 10 m high FFT column to analyze the effect of different amount of external loadings. To evaluate the
effectiveness of coke-capping over time, the modeling results were analyzed in terms of the dissipation of excess pore
water pressure, the development of effective stress, the reduction in void ratio, and the increase in solids content. Using
a 0.5 m thick coke layer over FFT, the effective stress, the void ratio, and the solids content achieved at the bottom of the
column after 1 year were found to be 3.4 kPa, 2.3, and 50%, respectively. Identical properties for the no-capping
scenario were found to be achievable after five years of deposition. The improved consolidation behaviour of the cokecapped FFT provides an alternative solution for oil sand tailings management.