Effect of compressibility on the stress state of wet and dry bauxite residue

The construction of filtered tailings storage facilities (TSFs) provides an alternative deposition strategy to mitigate the risk of liquefaction of loose and saturated hydraulically placed tailings through the processes of filtration and compaction. However, challenges in depositing and compacting filtered tailings can impede efforts to achieve unsaturated and/or dilative conditions. For example, it is shown that for the same compaction degree and initial void ratio, clays compacted wet of optimum moisture content (OMC) are more compressible than those compacted dry of OMC. Further, increasing stress in initially dilative soils can result in intersection of the normal compression line (NCL) with the critical state line (CSL), thereby transitioning from a dilative to a contractive state. To assess the effect of compressibility on this transition stress of filtered tailings, one-dimensional compression behavior of wet and dry compacted bauxite residue (red mud) was compared with the CSL for the same material. Soil-water retention tests were also carried out on one-dimensionally compressed samples to estimate the matric suction and effective stress while considering the effects of salinity in red muds. The results showed that for the same compaction conditions, dry filtered tailings transitioned from dilative to contractive conditions at lower transition stress than wet filtered tailings. The implications of these findings on minimizing the risks of flow liquefaction in filtered TSFs were outlined.