## 5 Discussion  
An original study with the objective of contributing to the understanding of the geochemical behaviour of a new form of iron ore tailings disposal (stacking of compacted filtered ore tailings-Portland cement blends) was presented as an alternative method to the conventional tailings dam disposal. Adequate correlations between the \(\eta/C_{\mathit{iv}}\) index with \(q_{\mathit{u}}\) and \(G_{0}\) through power functions were obtained (Figure 5). In artificially cemented soils the \(\eta/C_{\mathit{iv}}\) ratio is usually adjusted by a power (\(\zeta\)) applied to the variable \(C_{\mathit{iv}}\) (defined by curve fitting) to make the rates of variation of \(\eta\) and \(1/C_{\mathit{iv}}\) compatible [20]. The value of \(\zeta\) determines the greater or lesser contribution of porosity or cement content in the mechanical response. According to [PERSON] et al. [34], its magnitude is directly associated with the properties of the soil matrix and usually approximates the inverse of the exponent of the power function (\(\zeta\approx 1/D\) or \(1/E\) in Equations (2) and (3), respectively). In the present study, an assumed value of \(\zeta=1\) allowed the best fit (R\({}^{2}>0.92\)) for correlating the \(\eta/C_{\mathit{iv}}\) index with \(q_{\mathit{u}}\), \(G_{0}\) and durability. [PERSON] et al. [35], working with a residual soil of very low (or no) plasticity corresponding to a well graded silty sand and with three different grain size fractions of this same soil determined that, under conditions of similar mineralogy, the particle size distribution is the most relevant factor in the definition of the magnitude of \(\zeta\). The research concludes that soils with higher fines (silt) content, fine sand fraction, and better graded, with broader grain size distribution curves, reported lower power values (\(\zeta\approx 0.21\)) compared to poorly  
Figure 8: Stress–axial strain–volumetric strain curves for the consolidated drained triaxial tests of specimens moulded with (**a**) \(\gamma_{d}\) of 17 kN/m\({}^{3}\) and 3% of early strength Portland cement blended with iron tailings under confining pressures of 50, 100 and 200 kN/m\({}^{3}\) and (**b**) \(\gamma_{d}\) of 19 kN/m\({}^{3}\) and 3% of early strength Portland cement blended with iron tailings under confining pressures of 50, 100 and 200 kN/m\({}^{3}\). graded and fine to coarse sandy soil fractions (\(\xi\approx 1\)). However, mineralogical composition (related to particle shape) is reported as the most decisive factor in the magnitude of \(\xi\), reporting adjusted values of \(\xi=1\) and \(\xi=0.1\) when comparing two uniform sands (with similar particle size distribution) characterized by having majority quartz and mica phases, respectively. The preponderant contents of quartz and iron minerals (hematite and goethite) in the filtered iron ore tailings determine the value of the fitting power (\(\xi=1\)). Values of \(\xi=1\) have been widely reported in the literature for the definition of dosage equations in soils of granular or frictional nature treated with Portland cement [36]. This value, equal to unity, determines an equivalent influence between porosity and cement volumetric content on \(q_{u}\), \(G_{0}\) and durability. Adding cement is considered an effective procedure to prevent liquefaction of soils. In general, the behaviour pattern of filtered iron ore tailings-Portland cement blends is determined by brittle and strain softening behaviour at low confining stresses (mainly due to cementing agent bonds), which evolves to more gentle strain softening with peak strength occurring at higher axial strains as confining stress levels increase (Figure 8). This behaviour is analogous to that reported for a wide range of cemented sands tested at low confining stresses [37; 38]. The larger the \(\gamma_{d}\) of the compacted specimens (lower \(\eta\)), the larger the peak deviator stress reached, the stiffer and more dilative the material, and the greater the post-peak drop in the deviator stress.