Critical state analysis of two compacted filtered iron ore tailings with different gradings and mineralogy at different stages of treatment

Slurry tailings storage in large impoundments has been largely used worldwide for a long time, as their cost is very competitive. However, recent disasters have brought to light the need to better comprehend the mechanics of the materials stored and to search for disposal alternatives to overcome the drawbacks. One possibility is the filtered tailings disposal (dry stacking) which requires a better understanding of the material's response in a dewatered (through filtration) and compacted condition. This paper compares two tailings from the same beneficiation (treatment) plant with different gradings and mineralogy, related to the beneficial processes they undergo. A series of triaxial tests comprising isotropic compression without shearing specimens, as well as isotropic compression followed by drained (CID) and undrained (CIU) shearing, and K-compression followed by undrained (CKU) shearing specimens were conducted over a range of confining pressures and initial compaction degrees. The experimental program allowed the evaluation of convergence for normal compression lines (NCLs) and the analysis under the light of critical state soil mechanics for the stress-strain response of the tested materials. The research outcomes show that changes in iron ore tailings gradings due to different production processes and the use of different compaction degrees had an influence on its behavior (compression and shearing) at lower stress levels, while at higher stresses levels, this difference is erased and there is a convergence for unique and parallels NCL and CSL on & nu;-ln p & PRIME; plane with a spacing of 2.71. On the p & PRIME;-q plane both tailings showed a unique and similar CSL.