Effects of structure and pore-water chemistry on critical state behavior of bauxite residue

Differences in the fabric of reconstituted triaxial samples may increase the difficulty of achieving a unique critical state for some soils. Moreover, changes in the salt concentration of bauxite residue can result in non-unique critical state lines (CSLs). To evaluate the effects of fabric and pore-water chemistry on the critical state of bauxite residue, this paper compares the triaxial compression behavior of intact, slurry consolidated, and various forms of moist tamped samples, at a range of salt concentrations. The variations in fabric were also investigated using scanning electron microscopy and nuclear magnetic resonance (NMR) tests. The changes in pore-water chemistry were analyzed using X-ray methods and changes in salt concentration. The results showed that the particle agglomeration induced during reconstitution resulted in a more significant shift of the CSL than the decrease in salt concentration. Microimaging and shear behavior of samples showed that the slurry consolidation method may be the most suitable method for representing in situ behavior of clayey bauxite residue. NMR findings suggest that variations in water retained in the micropores of reconstituted samples stem from differences in microstructure. The implications of changes in salt concentration and sample microstructure on the design of clayey bauxite tailings storage facilities are discussed.