# The Experimental Characterization of Iron Ore Tailings from a Geotechnical Perspective
## 4 Discussion
When compacted in order to simulate the conditions of tailings used as a building material or in alternative tailings storage facilities (dry stacking, e.g.,), the tailings' behavior is qualitatively comparable to that of the reconstituted samples in similar conditions. But, as observed in conventional geomaterials, the stress-strain response of the compacted tailings is much more rigid, at least partially as a result of the much clearer tendency to dilate from earlier loading stages. In fact, the axial strains induced by deviatoric stress increases that would be expected in the field under conceivable undrained loading conditions (\(\Delta\)q \(\approx\) 100-500 kPa) are considerably smaller. As a result, the undrained Young's Modulus (E\({}_{\text{U}}\)) measured in the compacted sample rises from 11.6 to 252.1 MPa for a deviatoric stress increase of 100 kPa and rises from 13.3 to 119.0 MPa for a deviatoric stress increase of 500 kPa when compared to the non-compacted reconstituted samples. Similarly, under undrained cyclic triaxial loading, the features of behavior are also typically observed in sandy materials under comparable loading conditions. In fact, not only does every cycle cause increasing excess pore pressure, but also, as p' approaches near-zero values, the typical butterfly shape shown by the cyclic effective stress patch is established. Once again, the cyclic behavior of the material is governed by the same lines observed in undrained monotonic loading: the CrSL and the PhTL. In addition, the level of cyclic loading applied in each cyclic test strongly affects the response of the material, namely with respect to the number of loading cycles needed to reach liquefaction. The stress-strain response of the sample during undrained cyclic shearing also fits the typical behavior of conventional granular geomaterials, with large axial strains accumulating in each cycle, namely in extension, as liquefaction occurs. The behavior of the iron ore tailings tested under undrained cyclic loading can also be assessed through the progressive degradation of shear stiffness and variation in the damping ratio with increasing shear strain (Figure 11). As observed in conventional geomaterials, significant degradation of the shear stiffness and large damping variations can be observed as the shear strain progressively increases with cyclic loading. The shear stiffness degradation with shear strain (Figure 11a) shows behavior similar to that observed in common geomaterials, namely in sands, where cyclic-induced liquefaction causes a progressive but massive reduction in the shear stiffness with shear strain. With respect to the damping variation with shear strain (Figure 11b), the initial behavior is consistent with that observed in common geomaterials, with a progressive increase in damping being observed in each cycle. But as shear strains increase above around 2%, the shapes of the hysteretic shear stress-shear strain curves deviate from the common shape used to calculate damping based on elastic considerations, and the damping values obtained show significant reductions. Clarification of whether this is a specific feature of tailings or results from an inappropriate estimation of real damping values due to the shape of the stress-strain curves requires further testing and analysis. When assessing the liquefaction resistance of conventional granular geomaterials, when cyclically loaded in undrained conditions, it is common to represent the variation in the number of cycles required to reach liquefaction (N\({}_{\text{Liquefaction}}\)) against the cyclic stress ratio (CSR = \(\tau/\sigma^{\prime}\)v\({}_{0}\)) applied during the test, often assuming that liquefaction occurs when the double-amplitude axial strain measured in a cycle reaches 5% (5%DA).