# The Experimental Characterization of Iron Ore Tailings from a Geotechnical Perspective
## 3 Results
### Modified Proctor Test  
The compaction curve relative to the modified Proctor test for the iron ore tailings tested (Figure 6) was obtained following the procedures established by the ASTM standards [27]. The values of the optimum water content and the maximum dry unit weight were established as 8.95% and 2.99 g/cm\({}^{3}\), respectively.  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Plastic Limit—w\({}_{\rm P}\) (\%) 1** & **Liquid Limit—w\({}_{\rm L}\) (\%) 2** & **Plasticity Index—PI (\%)** \\ \hline
15 & 20 & 5 \\ \hline \hline \end{tabular} \({}^{\rm 1}\) ASTM D4318—17\({}^{\rm 1}\)[25]; 2 BS 1377-22022 [26].  
\end{table}
Table 1: Average plasticity characteristics experimentally determined for the iron ore tailings tested.  
Figure 6: Compaction curve obtained for the iron ore tailings tested using the energy defined for the modified Proctor test.  
The shape of the compaction curve, obtained with the modified Proctor test, is similar to the compaction curves usually found in conventional geomaterials, namely for those commonly employed in embankment construction. In fact, a peak is clearly defined in the curve relating the water content used in the compaction with the resulting dry unit weight. Also, the value of the optimum water content, which is about 60% of the plastic limit, is in line with the values observed in conventional geomaterials. For example, the optimum water content (wopt) can be correlated with the liquid limit (wL) as follows [32]:  
\[\mathrm{w_{opt}}=0.3802\mathrm{w_{L}}+2.4513 \tag{1}\]  
Equation (1), where wopt and wL are given in %, predicts a value of 10.1% for the optimum water content (wopt) of a geomaterial with a liquid limit (wL) of 20%, which is fairly close to the value experimentally determined.  
On the contrary, the value obtained for the maximum dry unit weight is much higher than the values commonly found in conventional geomaterials. For example, employing the database that was used to establish the correlation shown in Equation (1), the maximum dry unit weight (\(\mathrm{\gamma_{d}}^{\mathrm{max}}\)) can be correlated with the liquid limit (wL) as follows [32]:  
\[\mathrm{\gamma_{d}}^{\mathrm{max}}=2.116-0.01008\mathrm{w_{L}} \tag{2}\]  
Equation (2), where \(\mathrm{\gamma_{d}}^{\mathrm{max}}\) is shown in g/cm\({}^{3}\) and wL is given in %, predicts a value of 1.91 g/cm\({}^{3}\) for the maximum dry unit weight (\(\mathrm{\gamma_{d}}^{\mathrm{max}}\)) of a geomaterial with a liquid limit (wL) of 20%, which is much lower than the value experimentally determined. However, it should be noted that the large database (126 different soils with different plasticity and grain size compositions) used for establishing these correlations is only composed of conventional geomaterials, with specific gravity of soil solids (G) varying between 2.58 and 2.85. However, the iron ore tailings tested have a much higher value of the specific gravity of soil solids (G), which is much higher than the range of values exhibited by the materials included in the database. As a result, the values cannot be directly compared and the correlation proposed in Equation (2) is not applicable to the unconventional material tested in this research.