## 6 Discussion
Considering this, geomembrane SP2 and especially geomembrane SP3 could be very close to, or have already reached, their residual stages (the end of the first stage) for Std-OIT and HP-OIT, while SP1 is likely in the first stage. Figure 5: Variation in Std-OIT and HP-OIT comparing the samples based on the difference between the average values obtained in the tests after exposure and the OIT value presented in the GRI GM13 standard, with statistical errors shown. The results of the tensile tests, both at yield and break points, show that all the samples had average values that were satisfactory, considering the coefficient of variation (CV), when compared to the minimum values established by the GRI GM13 standard [45], and there is no statistically significant difference between them (Figure 7). This could suggest that despite the consumption of antioxidants and stabilizers in the geomembrane, no significant signs of physical degradation were observed in terms of a significant decrease in tensile strength properties. This would likely indicate that the material was still in the first (SP1) and second (SP2 and SP3) stages of the three-stage degradation model of geomembranes. However, when evaluating the results on the SCR, samples SP2 and SP3, which were exposed to climatic and chemical weathering conditions (tailings) for 11 years, had average values that were less than 50% of those established by the GRI GM13 standard [45] (Figure 8), which means that they reached nominal failure. Ref. [31], when analyzing HDPE geomembranes with different types of resin and under varying exposure conditions, suggests that a change in the SCR due to morphological changes may be an important factor contributing to its reduction in value. Other factors that may also contribute to the reduction in the SCR, according to the prior authors, include surface scratches, caused by installation damage, and/or surface oxidation. Figure 6: Generic HDPE geomembrane’s three stages of degradation based on Std-OIT and HP-OIT (adapted from [43]). Figure 7: Variation in break strength comparing the average values of the samples with 100% and 50% of the value presented in the GRI GM13 standard, with statistical errors shown. The SP-NCTL test was not conducted on either surface of the geomembrane (exposed or in contact with the dam), so it was not possible to determine whether the surface in contact with the soil had lower SCR values compared to the exposed surface. Therefore, it was not possible to rule out the possibility that surface scratches and/or surface oxidation contributed to the low SCR values. Ref. [31] observed a reduction in the SCR values before antioxidant depletion and before it was possible to observe evidence of geomembrane chemical degradation. The author related this fact to morphological changes during the aging process that were capable of affecting the inter-lamellar connections due to chain disentanglement. In chain disentanglement, the inter-lamellar connections of the crystalline lamellae decrease, and the material can become more prone to cracking. Ref. [34] states that the extent of these morphological changes will vary depending on the exposure conditions of the geomembrane, as well as the thermal and stress history experienced during the manufacturing process, which affects the orientation of the crystal lamellae. Therefore, the possibility that the reduction in the SCR was due to chain disentanglement cannot be ruled out. It is not possible to determine the main factor responsible for the decrease in the SCR values. It is important to note that even though the geomembrane may have reached its nominal failure based on the SCR values, this does not imply that actual failure of the geomembrane in the field application is imminent. Despite these low values, the geomembrane had not yet ruptured based on visual inspection. This behavior is consistent with findings presented in the literature, such as [31], who also evaluated an HDPE geomembrane exposed in a mining facility in a warm-hot climate.