Settlement of Tailings Slurries by Creep Compression

2004

Rick J. Chalaturnyk, Silawat Jeeravipoolvarn,

Analytical predictions of the rate and magnitude of settlement of deposited oil sands tailings slurries generally overestimate how fast pore pressures will dissipate. Field deposits of nonsegregating tailings to mature fine tailings show continued high pore pressures near the surface which impede surface reclamation. In geotechnical analyses which predict the consolidation behavior of soft soils a finite strain theory is used. Effective stress void ratio and permeability void ratio relationships determined from laboratory large strain consolidation tests are used in the finite strain predictions. This theory, however, cannot predict the full range of sedimentation, consolidation and pore pressure dissipation which occurs in large scale deposits of thixotrophic tailings slurries. A new large strain consolidation model which assumes that the creep rate of the slurry exceeds the pore pressure dissipation rate is being investigated. This model is relevant for rapidly deposited, low permeability thixotrophic slurries where the upwards drainage path increases by several metres a year such as in oil sand tailings ponds and CT deposits. The model will be verified by analyzing the 10m high column of mature fine tails at the University of Alberta which has been monitored for over 20 years and in which the excess pore pressures are still very high.

Keywords: Settlement, Creep, Thixotrophy, Tailings, Consolidation