## 4 Discussion  
### Effects of Biopolymers on Macroscale  
After longer curing times, the UCS of the XG-treated soil was generally higher than that of untreated GRS, indicating that extended curing time can effectively enhance the soil's stiffness. While short-term curing slightly reduced strength, the failure strain of the soil generally increased. The addition of LBG significantly improved compressive strength at different curing times, with an increase in content also leading to a rise in failure strain. This suggests that LBG enhances both the stiffness and toughness of the soil. Notably, in the 1.0% to 2.0% content range, the improvement in UCS was particularly significant, with the most notable effect at 1.5%. Adding LBG (especially at 1.5%) significantly enhanced the soil's compressive strength. However, when LBG content reached 2.0%, the strength improvement effect began to level off and even slightly decrease. When the content of guar gum is too high, it can make the particle surfaces overly smooth, increasing the relative movement or sliding between particles, which reduces friction. Excessive guar gum may not disperse uniformly, leading to the formation of localized colloid-rich regions. These regions of colloid are prone to deformation under compression, causing discontinuous interfaces within the soil, reducing the overall structural stability and leading to a decrease in compressive strength. As GG content increased, the UCS of the soil initially increased and then stabilized. At lower GG contents, the bonding effect of GG helped form a more stable particle structure, effectively resisting external forces and leading to a gradual increase in UCS. Once GG content reached a certain level, the soil particles became fully coated by GG. At this point, further increases in GG content had little effect on structural stability, and the UCS stabilized. The effect of XG content and curing time on the soil's compressive strength is not independent; rather, there is an interaction between these two factors. For instance, when the XG content is low, extending the curing time does not significantly increase the soil's compressive strength. Conversely, when the XG content is high, insufficient curing time fails to achieve ideal compressive strength. Understanding this interaction is crucial for optimizing the soil's compressive strength by controlling both XG content and curing time. The variation in LBG content shows a relatively stable trend in the soil's compressive strength across different curing times. For different LBG contents, as curing time increases, the soil's compressive strength steadily increases before reaching a point of stabilization. GG content and curing time are also interrelated, impacting the soil's compressive strength. When GG content is low, extending the curing time does not significantly improve compressive strength. However, when GG content reaches a certain level, insufficient curing time limits the potential improvement in compressive strength. Thus, an in-depth study of the interaction between GG content and curing time is necessary to effectively enhance the soil's compressive strength. The UCS of GRS treated with different biopolymers is shown in Figure 17. As the curing time increases, the UCS of both the untreated GRS and the soils modified with XG, LBG, and GG generally exhibit an upward trend. Specifically, the effect of XG on GRS shows some fluctuation. During the early curing period (e.g., 0 and 3 days), the UCS of the XG-treated soil is lower than that of the untreated soil. This could be attributed to the fact that the addition of XG disrupts the hydration process of the soil particles, weakening the bond between them and thus reducing the compressive strength. However, as the curing time progresses, the beneficial effects of XG begin to emerge. Notably, after 3 days of curing, an improvement is observed.