## 4 Discussion
### Effects of Biopolymers on Macroscale
After 14 days, the UCS of the soil with 1.5% XG is significantly higher than that of the untreated GRS, indicating that XG at this concentration can substantially enhance the soil's compressive strength. This improvement is due to the formation of a dense network structure between the XG molecular chains and the soilparticles, which effectively increases the soil's bearing capacity. Additionally, the hydroxyl (-OH) and ether bonds (-O-) in the XG molecules interact with free iron oxide particles in the GRS, strengthening the bonding force between particles and consequently enhancing the compressive strength. LBG significantly enhances the UCS of GRS. Throughout the curing periods, the UCS of the modified soil increases as the content of LBG rises. Specifically, after 14 days of curing, the compressive strength of the soil modified with 1.5% LBG is substantially higher than that of the untreated soil, demonstrating the positive effect of LBG in improving the compressive strength of GRS. LBG forms a \"network\" structure with soil particles through physical adsorption, hydrogen bonding, and electrostatic attraction, thereby improving the bond between soil particles and increasing the soil's compressive strength. The sugar and hydroxyl groups in the LBG molecules interact with the hydroxyl groups on iron oxide particles, further enhancing the bonding between soil particles and improving the moisture retention capacity. The combination of LBG with free iron oxide results in a more compact and stable soil structure, ultimately enhancing its compressive strength. GG also affects the UCS of GRS to varying degrees depending on the curing time and concentration. As both the curing time and GG concentration increase, the compressive strength of the modified soil improves significantly. After 14 days of curing, the UCS of the soil modified with 2% GG is noticeably higher than that of the untreated soil, indicating  
Figure 17: UCS of biopolymer-treated GRS: (**a**) 0; (**b**) 3; (**c**) 7; and (**d**) 14 days. the significant role of GG in enhancing the compressive strength of GRS. The molecular structure of GG, rich in hydroxyl and sugar groups, interacts with iron oxide particles similarly to LBG, substantially increasing the soil's compressive strength. In conclusion, under appropriate concentrations and curing times, XG, LBG, and GG can all effectively enhance the UCS of GRS. Among these, GG provides the most significant improvement at higher concentrations and longer curing times, while LBG shows a relatively stable enhancement across all curing stages. XG, on the other hand, improves soil compressive strength most effectively with longer curing times and optimal concentrations. Overall, as the curing time increases, the compressive strength of the soil modified with various biopolymers tends to increase. Under the same curing time, soils modified with LBG and GG generally exhibit higher compressive strength, whereas soils modified with XG show lower compressive strength. These differences may be attributed to the unique chemical structures and properties of the biopolymers, which lead to varying interaction mechanisms with GRS and consequently affect the soil's mechanical properties. The mechanisms by which these biopolymers affect the soil's E-value are closely related to their molecular structure and chemical properties. The effect of biopolymers on the E-value of different soils also shows distinct differences [35; 39]. The molecules of XG have a unique helical structure, which may require time to adjust during the short-term curing period in order to interact with soil particles, leading to complex changes in the E-value. After long-term curing, XG can effectively fill the voids between soil particles, enhancing the connections between particles and improving the soil's stiffness. In contrast, the molecular structures of LBG and GG are more favorable for tightly binding with soil particles during the early stages of curing, resulting in a higher E-value at the beginning of the curing process.