# The Experimental Characterization of Iron Ore Tailings from a Geotechnical Perspective
## 5 Conclusions  
The mining industry produces large amounts of valueless tailings with significant economic, social and environmental risks to society. Ensuring the safety of massive tailings storage deposits and implementing the principles of circular economy by using these  
Figure 12: Liquefaction resistance (5%DA) of the tailings tested in comparison to other mineral sand tailings [34] and natural Sile sand [35]. unconventional geomaterials in geotechnical works to reduce this problem and the wide-ranging impacts of raw materials' extraction is therefore a critical goal of the mining industry. This paper focuses on the experimental characterization of iron ore tailings, which are the most abundant type of mining waste produced in the world. The results presented highlight the most relevant aspects of behavior of iron ore tailings, which behave as follows:  
* They qualitatively behave like other conventional geomaterials with similar grain size composition, in the range of silts and sands, and low plasticity;
* They are distinct from natural soils, with the composition and shape of the grains more or less significantly affecting the values of some relevant properties;
* They exhibit compaction characteristics typical of conventional geomaterials, with large dry unit weights being a consequence of unusually high G values that result from the remaining presence of iron particles;
* They considerably benefit from the improvement induced by compaction, namely with respect to the stiffness and straining-induced dilation observed in undrained monotonic triaxial compression, with intrinsic shear resistance (\(\phi\)') being high in any case;
* They present large shear stiffness degradation and large damping variations under undrained cyclic loading causing liquefaction, with the behavior strongly depending on the cyclic stress ratio applied;
* They show liquefaction resistance similar to other comparable tailings and possibly larger than natural sands. Overall, iron ore tailings can be described as granular materials, with a significant silty component that is responsible for the low plasticity observed, combining higher effective shear resistance and very high maximum dry unit weight after compaction with some susceptibility to earthquake-induced liquefaction, as a result of the following characteristics of tailings particles:  
* Large resistance which is due to the fact that tailings result from the mechanical crushing and grinding of rocks, which tend to form particles with an angular shape that considerably differs from the spherical shape of natural soils particles, as observed in optical and electron microscope photographs;
* Larger than expected values of the maximum dry unit weight which result from the presence of iron particles in the tailings. The outcome of this research suggests that the characterization of iron ore tailings' behavior requires a geotechnical approach that does not overlook the particular and singular features of tailings particles shape and composition. Based on the results obtained, iron ore tailings seem to have promising behavior for applications as building materials in the field of geotechnical engineering. In fact, the consequences of the singularity of iron ore tailings grains with respect to the higher effective shear resistance and very high maximum dry unit weight after compaction should be explored for specific geotechnical applications where these unique properties are relevant. This includes applications where, namely after compaction, the following aspects apply:  
* High shear resistance and stiffness, at least partially due to the uncommon shape of tailings particles, are required (e.g., embankments);
* Large unit weights, due to the presence of iron particles that result in unusually high G values, can be an advantage (e.g., sea shore protection).