Undrained Strength of Deposited Mine Tailings Beds: Effect of Water Content, Effective Stress and Time of Consolidation

An understanding of the geotechnical behaviour of mine tailings is imperative when evaluating the stability and erosional resistance of sedimented tailings beds; as well as for the design and long-term management of tailings disposal facilities. Laboratory testing was conducted on mine tailings beds of various ages and thicknesses, deposited from concentrated slurries. Measured index properties allowed classifying the tailings as a coarse grained and non-cohesive material. The results obtained from the performed sedimentation experiments showed that the primary consolidation of the tailings beds was complete in approximately 1 h and negligible volume changes occurred in the beds during secondary compression. The undrained shear strength of the tailings beds was measured using an automated fall cone device at a depth interval of 1 cm and a profile of the shear strength variation with depth was obtained. At each tested surface, moisture content specimens were taken to determine the moisture content profile of the tested tailings beds. The undrained shear strength of the beds varied between 0.008 and 0.975 kPa for effective stresses below 1.19 kPa and increased with depth. Correspondingly, the moisture content decreased with depth and varied between 17 and 27%. The factor controlling the undrained shear strength of the tested beds was the vertical effective stress, with the water content also having some secondary effect. The correlation between the undrained shear strength and the vertical effective stress was expressed with a second order polynomial function. Consolidation time did not appear to influence the observed shear strength.