## 3 Test Results and Analysis
### Effect of Biopolymer on Compressive Strength
#### 3.1.1 Unconfined Compressive Strength  
Figure 6 illustrates the effect of biopolymer binders on the UCS of GRS after 14 days of curing, at different contents. Both before and after treatment, the stress-strain curves of GRS exhibited strain-softening behavior, indicating that the addition of biopolymers did not significantly alter the soil's mechanical behavior. Although the stress-strain curves generally displayed a strain-softening trend, the degree and characteristics of softening  
Figure 5: Experimental process for preparing biopolymer improved soil. varied with different biopolymer contents. At low biopolymer content, the strain-softening phenomenon was more gradual. However, as the biopolymer content increased, the rate of decline after reaching peak stress accelerated. The value of \(\Delta\) in the figure indicates the difference in unconfined compressive strength between the soil treated with biopolymers and the untreated soil. The unconfined compressive strength of soil treated with biopolymer at different contents is shown in the line chart in Figure 7, and the unconfined compressive strength increment between the current and previous content is shown in the bar chart in Figure 7. Under short-term curing, the UCS of GRS treated with XG initially decreased, then increased, and finally decreased again as the XG content increased. After longer curing periods, the UCS followed a trend of first decreasing and then increasing with the increasing XG content. The effect of XG content on the strength of GRS differed from that observed in other types of soil [32], suggesting that the influence of XG varies across different soil types. As LBG content increased, the compressive strength of GRS initially increased and then decreased, peaking at 1.5% LBG content. The addition of LBG enhanced the strength of both GRS and other types of soil, though the growth trends varied [33]. As GG content increased, the compressive strength of GRS generally showed an upward trend for the same curing times. The effect of GG on different soils varied, but it generally improved soil strength [34], which is consistent with the findings of this study. However, for some soils, low levels of GG may reduce strength [15]. The strain value corresponding to peak intensity increased after treatment with XG, and the rate of stress decrease in XG-treated soil was slower than in untreated soil. This study confirms that the reinforcing effect of XG and LBG in GRS has an optimal content, consistent with previous research [35]. This indicates that the reinforcing effect of biopolymers on soil does not necessarily improve with higher addition amounts. The observed trends in GRS are important for practical en  
Figure 6: Stress–strain curves of biopolymer-treated soil: (**a**) XG; (**b**) LBG; and (**c**) GG. gineering applications. For instance, in road foundation solidification, the optimal amount of biopolymer can be determined based on the required strength, ensuring project quality while minimizing material waste. The unconfined compressive strength of soil treated with biopolymer at different curing times is shown in the line chart in Figure 8, and the unconfined compressive strength increment between the current and previous curing times is shown in the bar chart in Figure 8. Regardless of the XG content, the UCS of the soil gradually increases with curing time. In the early stages, the growth in compressive strength is relatively slow. As curing continues, the internal particle structure of the soil gradually stabilizes, resulting in progressive increases in strength. When LBG content is fixed, the UCS of the soil shows an overall upward trend with extended curing time. In the initial curing stage (0-3 days), strength increase is slow due to incomplete reactions between LBG and soil particles. Between 3 and 7 days, the strength growth accelerates, indicating that physical and chemical reactions between LBG and soil particles intensify, thereby stabilizing the soil structure.