# The Experimental Characterization of Iron Ore Tailings from a Geotechnical Perspective
## 4 Discussion  
The results presented in detail in the previous section highlight the most relevant aspects of behavior of the iron ore tailings tested, which were collected from a Portuguese  
Figure 10: Stress–strain shear resistance response of a reconstituted sample isotropically consolidated to an effective confining stress of 200 kPa under undrained cyclic triaxial loading with \(\Delta\)q = \(\pm\)60 kPa: (**a**) effective stress path; (**b**) stress–strain response; (**c**) variation in the effective stress ratio with p’; (**d**) variation in the excess pore pressure with axial strain. iron mine located in Torre de Moncorvo. These tailings should be, at least qualitatively, representative of other iron ore tailings present in the world, as the extraction, beneficiation and depositional procedures used in iron mining around the world are fairly comparable. Firstly, reconstituted samples were prepared based on the slurry deposition method, which tends to more effectively replicate the field depositional conditions observed in many tailings storage facilities, namely in tailings dams. Because these geotechnical structures are usually the most prone to failure, it was reasonable to select this reconstitution method to address tailings' mechanical properties, namely those that depend more on the conditions and structure of the samples and/or that are more relevant to stability analysis. In fact, this method results in uniform reconstituted samples that truly replicate field behavior [30], provided that the correct amount of water is used during reconstitution to avoid segregation. In addition, its use has been proven successfully, namely when preparing reconstituted samples with complex geometry [22], which is another advantage of the method. With respect to the physical and identification properties, the iron ore tailings tested can be described as a transitional uniform material composed of very similar percentages of silt and sand, exhibiting limited but non-negligible plasticity (IP = 5). It is in fact the plasticity of these tailings that supports the use of the slurry deposition method. But because the difference between the liquid and the plastic limits is relatively small, the liquid limit could only be assessed using the cone penetrometer method (multipoint) defined by the BS standards [26]. But the most remarkable feature of the iron ore tailings tested is the unusually high values observed for the specific gravity of soil solids (G \(\approx\) 4.7), which considerably exceed the values commonly observed in conventional geotechnical materials (G \(\approx\) 2.6\(\sim\)2.7). Even if these values can vary more or less significantly depending on the amount of iron left in the tailings, which reflects the particular efficiency of the beneficiation process during mining that depends on the mine and on the historical period, the values of the specific gravity of soil solids and other index properties of iron tailings that are directly correlated (unit weight, e.g.,) tend to show values that are often much higher than those commonly found in soils. The value of G obtained in this case reflects the fact that the tailings tested were produced about 50 years ago and using fairly primitive manual selection procedures. Overall, the values obtained for the samples tested are comparable to those found in other mining sites, e.g., in Yuhezhai iron ore tailings [31]. Furthermore, except for the values of G, the values obtained fit into the ranges commonly observed in conventional geotechnical materials. This suggests that the experimental characterization of iron ore tailings should be established based on a geotechnical perspective, without overlooking the particular features of tailings' compositions. But if iron ore tailings are to be used as a construction material in geotechnical works, the tailings are expected to be compacted in order to improve their mechanical behavior, except in very specific conditions of application.