# Mechanical Behavior of a Mine Tailing Stabilized with a Sustainable Binder
## 4 Mechanical Behavior of Mine Tailing after Stabilization
### Results Analysis
#### 4.3.2 CU Triaxial Tests  
The evolution of the deviatoric stress (q) with the axial strain (\(\varepsilon_{\text{a}}\)) for the alkaline-activated tailings specimens is shown in Figure 19. The increase in the confining stress resulted in a respective increase in the q values. The values of q obtained for stabilized specimens resulted in considerably higher resistances, showing the effects of the geopolymerization mechanism on the mechanical resistance of the mine tailing. All the specimens showed a peak and residual deviatoric stress, with greater development of q between \(0<\varepsilon_{\text{a}}<0.2\%\), except for the specimen subjected to a confining stress of 200 kPa, whose test was interrupted with an axial strain level of 4.5%, due to a break in the laboratory's electrical supply. From the comparison of the failure stresses resulting from the uniaxial tests and the peak deviatoric stresses resulting from the triaxial tests, both carried out in specimens with a curing period of 7 days, it is possible to observe the influence of the application of different confining stresses. The stabilized samples with the alkaline cement submitted to different values of \(\sigma_{3}\) revealed much higher peak deviatoric stresses than the failure stresses obtained through uniaxial tests, highlighting the impact of confining stress on the strength of the tailing-binder mixtures.  
Figure 20 shows the evolution of pore pressure (\(\Delta\)u) with axial strain (\(\varepsilon_{\text{a}}\)) for the improved specimens. It was observed that all specimens showed an overconsolidation-typical behavior, showing a contracting tendency (\(\Delta\)u > 0) during the first phase of the test and a dilating tendency (\(\Delta\)u < 0) during the rest of the test. This behavior indicates that the specimens manifest an excess of pore pressure until the development of their maximum mechanical resistance up to failure, followed by the dissipation of the excess pore pressure and consequent dilation of the specimens. The peaks observed along the curves are due to the loading and unloading cycles performed.  
Figures 21 and 22 show the resulting stress trajectories regarding total and effective stresses. It can be observed that for all the specimens, in terms of effective stresses, the trajectories tend to the right. This stress development confirms the overconsolidation and the dilating behavior of these specimens. From the stress trajectories, the failure points of each of the specimens were identified once again, thus allowing us to trace the failure envelopes of the stabilized mine tailings. This analysis was performed for peak and  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Parameters**} & \multicolumn{2}{c}{**NCL**} & \multicolumn{2}{c}{**CSL**} & \multicolumn{2}{c}{**K-Line**} \\ \cline{2-7}  & \(\lambda\) & **N** & \(\lambda\) & \(\Gamma\) & **k** & \(\
u_{\text{k}}\) \\ \hline Natural MT & 0.101 & 2.2795 & 0.102 & 2.2771 & 0.01000 & 1.6856 \\ \hline Stabilized MT & 0.024 & 1.9100 & 0.024 & 1.8705 & 0.00038 & 1.7526 \\ \hline \hline \end{tabular}
\end{table}
Table 6: Parameters of the critical states theory before and after stabilization.  
Figure 19: Evolution of the deviator stress with axial strain (stabilized specimens).  
However, there was a considerable increase in the friction angle, both in total and effective stresses, for the tailing-binder mixture studied. The considerable increase in the friction angle after the stabilization of the tailings may be related to the addition of a considerable percentage of fly ash to the mixture, which contributes to a better filling of the voids existing between the particles of tailings, resulting in a more compacted matrix, with the consequent increase in the friction angle.