## 4 Results and Discussion
### Field and Laboratory Test Results  
Laboratory characterization tests, as shown in Figure 5 and summarized in Table 1, revealed that most samples consisted predominantly of sands or silts as their primary and secondary components. The average D\({}_{50}\) fell within the order of magnitude of 10\({}^{-2}\) mm, a typical value associated with silts and fine sands. Of all the samples, 66% displayed no plasticity limit, while among the remaining 33%, 80% exhibited a plasticity index ranging between 7 and 15, signifying an intermediate level of plasticity.  
To provide a more detailed description of the materials under investigation, please refer to Table 1. This table presents a detailed summary of the laboratory test results, organized according to the structures studied. Specific gravity (SG) values ranged between 2.82 and 4.77, with most samples displaying no noticeable plasticity index. [PERSON] et al. [43] classified iron ore tailings from the Iron Quadrangle as predominantly silty sand, with a specific gravity of solids of 2.92. Similarly, [PERSON], [PERSON] and [PERSON] [44] concurred, characterizing most of the Iron Quadrangle iron ore tailings as primarily silt or sand, and their specific gravity was 3.71. In contrast, [PERSON] et al. [45] identified the iron ore tailings from the Fundao Dam as predominantly clayey silt. Additionally, [PERSON] et al. [46], in their investigation of Brumadinho Dam tailings, determined them to be primarily composed of sands and silts, with specific gravity values ranging from 2.43 to 4.86. The liquid limit (LL) and plastic limit (PL) of the samples were established, revealing that Structure 1 exhibits plastic behavior, whereas the other structures, owing to their larger particle sizes, exhibit minimal or negligible plasticity.  
The material classification index (I\({}_{\text{c}}\)) calculated from field tests (Equation (6)), illustrated in Figure 4, varies from 2.05 to 4, indicating a very heterogeneous material, with layers of sandy, silty, clayey, and even organic material, according to [PERSON] [39]. Apart from the laboratory tests that characterize the collected samples, SCPTu tests can only infer of the materials behavior, since no samples are extracted. The pore pressure ratio (B\({}_{\text{q}}\)) (Equation (2)), also shown in Figure 5, varies from 0 to 1, with approximately all readings comprehended in the interval of 0 and 0.5, which could already indicate a partial drainage condition.  
Figure 5: Particle size distribution curves for the three structures: (**a**) Structure 1, (**b**) Structure 2, and (**c**) Structure 3 under study, revealing that the predominant material composition consists of a combination of sands and silts.  
Triaxial tests yielded cohesion (_c_) intercept results ranging from 0 to approximately 50 kPa, with a mean value of 10.71 kPa and a median of 5 kPa. Additionally, the friction angle (\(\phi\)) results spanned from 21\({}^{\circ}\) to 37\({}^{\circ}\), with a mean value of 32.09\({}^{\circ}\) and a median of 36\({}^{\circ}\). Figure 6 illustrates a representative result, displaying the Mohr circle along with the obtained Mohr-Coulomb parameters. The observed range of variation in the Mohr-Coulomb parameter results is consistent with those reported in the literature for copper and iron tailings [47]. [PERSON] et al. [7] investigated the Fundao Dam, reporting friction angles ranging from 28\({}^{\circ}\) to 36\({}^{\circ}\), classifying the tailings as cohesionless sands. In a separate study, [PERSON], [PERSON] and [PERSON] [48] examined the tailings from the Germano Dam (Iron Quadrangle region), finding friction angle values that varied from 28\({}^{\circ}\) to 37\({}^{\circ}\). [PERSON] [49] conducted research on tailings from four different dams in the Iron Quadrangle region and documented friction angle results spanning from 26\({}^{\circ}\) to 45\({}^{\circ}\) for the material, along with observations of low or negligible cohesion.