Consolidation – creep modeling of pilot data on deposition of flocculated fluid fine tailings

ABSTRACT: Pilot studies of flocculated fluid fine tailings (fFFT) deposits are modeled using coupled large strain consolidation – creep formulations embedded in the UNSATCON software. The creep formulations employed are based on theory developed by Vermeer, a hypothesis B type model that implies a strain rate dependency on the location of the compressibility curve, and Yin and Graham model that has been formulated using the concepts of equivalent time. The pilots comprised deposits of tailings placed in 13 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 two different models to simulate 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 excess pore-water pressure), compared to the consolidation only results, though agreement in still not perfect. Using different groups of plausible parameters 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.