# The Experimental Characterization of Iron Ore Tailings from a Geotechnical Perspective
## 4 Discussion
The results of the liquefaction resistance of the samples of iron ore tailings tested are plotted in Figure 12, with the results being compared with the liquefaction resistance of mineral sand tailings [34] and a natural sand, namely Sile sand [35], tested under fairly comparable conditions. The results show that the iron ore tailings tested have a liquefaction resistance that exceeds that of the mineral sand tailings presented for large values of CSR, but the resistance increase with decreasing CSR values is less pronounced. In addition, both tailings show higher liquefaction resistance than natural sands, including Sile sand (Figure 12), possibly due to the uncommon shape of non-natural tailings particles. Overall, the behavior observed, namely in terms of liquefaction resistance, is closer to that of sands, despite some plasticity of the tailings tested. This signals the need to address the possibility of earthquake-induced liquefaction occurrence in iron tailings, eventually considering energy-based methods that tend to more effectively explain the behavior of conventional granular geomaterials [19]. Figure 11: Analysis of the undrained cyclic triaxial tests on iron ore tailings with CSR values of 0.15 and 0.5: (a) shear stiffness degradation with shear strain; (b) damping variation with shear strain. Based on the results obtained, iron ore tailings seem to have promising behavior for application as a building material in the field of geotechnical engineering. In fact, the effectiveness of compaction in increasing the stiffness of tailings in undrained monotonic compression is quite promising and should be accompanied by a significant increase in the liquefaction resistance, similarly to what is observed in granular soils, where densification is a valuable liquefaction resistance measure [36]. In addition, the further light shed on the behavior of the tested unconventional geomaterial will support the more accurate analysis of existing and new tailings storage facilities, which will enhance the safety of these massive structures and reduce the possibility of dramatic consequences that result from their failure. But if tailings need to be assessed from a geotechnical perspective, they are not natural soils. Actually, a true understanding of tailings' behavior requires the solid and openminded interpretation of the results, where the specific nature of tailings must not be ignored, namely with respect to the composition and shape of its grains. In this case, apparently, too-large values of the effective angle of friction or the maximum dry unit weight look more reasonable when a detailed understanding of the particular features of tailings is achieved. Nevertheless, a final but important recommendation must be issued, namely when considering the use of iron ore tailings as a sustainable building material. Indeed, sustainable geotechnical solutions can only be achieved when using unconventional geomaterials, particularly waste, if the environmental impacts of using these materials are fully under control. Therefore, real applications of iron ore tailings and other similar types of waste require previous analysis of their physicochemical and ecotoxicological properties to confirm the environmental safety of their use in the particular projected conditions [10; 11].