## 3 Results  
### Assessment of the Mechanical Behavior (Strength and Stiffness) of Novel Geomaterials  
A comparative analysis is presented below for the eight mixtures involved in the study, considering both unconfined compressive strength and stiffness results. Due to the presence of 3% and 6% cement contents in the mixtures with residues (CLW, GY, and GG), these were grouped according to the percentage of residue added by weight of the clay soil. To simplify the comparative analysis, the optimal dry density (\(\gamma\)d = 17.6 kN/m\({}^{3}\)) was used as a common reference point, allowing a clearer observation of the effect of each treatment on the mechanical properties evaluated. The compressive strength and stiffness results are presented in Figures 9 and 10, respectively. As shown in Figure 9, the results indicate that GG exhibited the best performance in terms of unconfined compressive strength, reaching values up to 2335.97 kPa, particularly at a 20% dosage combined with 6% cement. GY also demonstrated notable improvements, achieving 2079.96 kPa under similar conditions. In contrast, CLW showed a less efficient response; the 15% CLW mixture outperformed the 30% mixture, suggesting a possible saturation effect or lower reactivity of the residue at higher contents. The associated standard deviations reveal greater variability in CLW and GY compared to GG, emphasizing the consistent performance of the latter. Regarding XG and XG-PPF, a progressive increase in strength was observed with increasing XG content, reaching a maximum of 859.59 kPa. The addition of polypropylene fibers (XG-PPFs) further enhanced mechanical behavior, achieving 1109.15 kPa at 5% XG, surpassing several cemented residue mixtures. These formulations also displayed the lowest standard deviations, indicating more homogeneous behavior. Although their strength was lower than that of GG or GY mixtures, their stabil  
Figure 8: Test set-up of stiffness and unconfined compressive strength. ity and sustainability position them as a viable alternative in contexts where mechanical uniformity and environmental considerations are prioritized. In terms of initial small-strain stiffness (Figure 10), GG again delivered strong results, with values reaching up to 7121.27 kPa at 20% content and 6% cement. However, unlike in the compressive strength data, the 10% GG mixture with 6% cement (6579.96 kPa) showed a slightly closer performance, indicating a more gradual increase in stiffness with increasing residue content. GY followed a similar pattern, with stiffness peaking at 8051.67 kPa for the 20-6%C mixture. Notably, these values represent the highest stiffness recorded across all formulations, suggesting that GY's reactivity and matrix formation at early strain levels are highly efficient under cemented conditions. CLW, whil  
Figure 10: Stiffness of eight stabilized soil mixtures compacted at optimal dry density (\(\gamma\)d = 17.6 kN/m\({}^{3}\)). The mixtures include construction residues (CLW, GY, GG) with 3% and 6% cement, XG, and XG–PPF. Figure 9: UCS of eight stabilized soil mixtures compacted at optimal dry density (\(\gamma\)d = 17.6 kN/m\({}^{3}\)). The mixtures include construction residues (CLW, GY, GG) with 3% and 6% cement, XG, and XG–PPF. stiffness (6223.88 kPa at 15-6%C), maintained the same trend observed in strength: limited improvement at higher residue content. The decrease in variability at 30% CLW compared to 15% (despite lower average stiffness) indicates a more consistent internal structure, albeit with reduced mechanical output. For the biopolymer-treated soils, XG and XG-PPF mixtures exhibited significantly lower stiffness values compared to cemented residues, with maximum values of 1709.94 kPa (XG) and 2197.75 kPa (XG-PPF) at 5% dosage. Nevertheless, the increasing trend with dosage was clear in both cases, and the incorporation of PPF provided a notable improvement over XG alone. The progression from 1% to 5% XG-PPF represented a near doubling in stiffness, emphasizing the positive synergistic effect of fiber reinforcement.