## 3 Analysis and Discussion of Test Results
### Analysis of Unconfined Compressive Strength Results  
The relationship between the amount of geopolymer incorporated and the unconfined compressive strength in the solidified soil is illustrated in Figure 8. It is evident that the compressive strength of the solidified soil with different amounts of geopolymers added during different curing periods is higher compared to that of the plain soil. The gelatinous substances C-S-H and C-A-S-H, formed through the hydration reaction of geopolymers, have a cementing effect on solidified soil. They fill the gaps between soil particles, resulting in improved soil stability and strength. During the initial stage, the hydration reaction of the geopolymer is not fully developed, resulting in a gradual increase in solidification strength. However, as the curing age progresses, the geopolymer continues to undergo a hydration reaction, leading to a further enhancement in the compressive strength of the solidified soil. The compressive strength of the consolidated soil is highest at a curing age of 28 days and a geopolymer content of 20%, reaching 570.86 kPa. Compared to the plain soil and the stabilized soil mixed with 25% geopolymer at the same age, the strength increased by 400.82 kPa and 28.34 kPa, respectively. The compressive strength of the solidified soil initially increases and then decreases with the addition of geopolymers at the same age. This is because initially, the amount of geopolymer added is small and the gelled substances produced by the hydration reaction of geopolymer are relatively small. If the amount is insufficient, the particle gap filling is inadequate, and the strength of the solidified soil increases as the amount of geopolymer added increases. However, the strength of the solidified soil decreases when the amount of geopolymer added is 25% compared to when the addition amount is 20%. This decrease is attributed to the increase in mass proportion of geopolymer in the solidified soil, which leads to a decrease in the net content proportion of loess. Consequently, the loess skeleton is reduced. Additionally, the gelled material, which forms clumps and covers unneacted steel slag and fly ash, is unable to effectively fill the voids between the soil particles and adhere to the soil surface. As a result, the overall strength of the solidified soil is diminished. The cured compressive strength increases with the extension of the curing age and reaches its maximum value at 28 days. When the geopolymer content is 25%, the compressive strength of the solidified soil is 2.12 times that of the 7-day curing period and 1.73 times that of the 14-day curing period at a curing age of 28 days. Similarly, the unconfined compressive strength of the solidified soil at a curing age of 28 days is 2.11 times that of the 7-day curing age and 1.6 times that of the 14-day curing age. These test results demonstrate that both the curing age and the amount of geopolymer significantly affect the strength of the consolidated soil. Figure 7: Internal friction angle and cohesion of solidified soil. (**a**) Change in angle of internal friction of solidified soil in the geopolymer. (**b**) Change of cohesiveness of solidified soil in the geopolymer. During the 28-day curing period, [PERSON] et al. discovered that when recycled fine powder (RFP) was added at a rate of 15%, the solidified loess exhibited the highest compressive strength, reaching 357.7 kPa [40]. [PERSON] et al. conducted a reinforcement test using an F1 ion-curing agent and determined that the maximum unconfined compressive strength of the tested loess was achieved when the dosage of the F1 curing agent was 0.3 L/m\({}^{3}\), reaching 280 kPa [41]. [PERSON] et al. utilized a wood calcium-source EICP solution to solidify roadbed loess and observed an increase in unconfined compressive strength to 232 kPa [42]. [PERSON] et al. employed a 20 be composite modified water glass for loess reinforcement, resulting in an increase in unconfined compressive strength to 287 kPa [43].