Transitional Oil Sands Tailings’ Filterability and Consolidation Behavior

Over the past few decades, the oil sands mining industry has taken steps to find ways to speed up the filterability and consolidation of their tailings deposits, which would otherwise take decades to settle and reach the required strength. The initiative has led to deposits that are combinations of sands and fines (<44 µm) in proportions whose geotechnical behaviors have not yet been determined by the existing body of knowledge. The purpose of this study is to examine how the quantity of fines and their index characteristics affect the filterability and consolidation of particular deposits. Findings from this research show that these deposits exhibit characteristics of low-plasticity soils. The hydraulic conductivity of these materials is strongly influenced by the fines content. The deposits behave more like sand below a threshold point of about 35 percent fines content, and they exhibit low hydraulic conductivity above this point. Furthermore, the hydraulic conductivity of these deposits is influenced by other factors, including clay properties, sodium adsorption ratio, and effective stress. The results of finite-strain consolidation modeling show that mixtures of sand and fluid tailings with fines within the threshold range exhibit significantly improved consolidation performance. In particular, compared to the performance of traditional fluid tailings deposits, settlement time and depth are reduced by more than 50%, and the time needed for complete pore pressure dissipation is reduced by more than 80%. Findings from this study provide an insight to the industry on the optimal fines–sand blending proportions for best performing deposits. Since these findings are solely laboratory-based, it should be noted that the determined threshold fines content and consolidation behavior may alter in field-scale deposition.