Influence of Shear Rate on Peak and Post-Peak Strength from Laboratory Vane Tests on Iron Ore Tailings

Laboratory-scale vane tests were performed on iron ore tailings (IOT), which are fine-grained tailings with higher permeability than natural clays, to investigate the effect of shear rate on measured shear strengths. IOT was prepared at different void ratios by slurry consolidation, with vane shear tests then conducted at peripheral velocities ranging from 20 to 200 mm/min. The post-peak strength was measured at rotation angles of 180° and 360°, which are relatively small compared to multiple revolutions (i.e., 3,600° or more) typically required for full remolding. The peak and post-peak shear strengths were significantly influenced by the peripheral velocity, transitioning from being viscous-dominated to partially drained behavior. Viscous effects predominantly dominated the shear strength at higher peripheral velocities and lower rotation angles, whereas partial drainage effects became more prominent when using lower shear rates, higher rotation angles, and lower void ratios. A transition from viscous-dominated to partially drained behavior was observed with decreasing void ratio, associated with an increased coefficient of consolidation. The Blight/Chandler approach was shown to be effective in assessing the effects of drainage parameters on measured strength. These findings highlight the critical need to select material-specific rates of rotation to accurately characterize the shear strength of fine-grained tailings.