## 4 Conclusions  
This study aimed to investigate the feasibility of solidifying loess by using steel slag-fly ash as the main raw material in an alkaline environment of water glass for hydration to form gelled material. The study included various tests, such as unconfined compressive strength, direct shear, compaction, disintegration, and XRD and SEM analysis. The effects of different geopolymer additions and curing ages on the solidified soil are considered. Based on the test results, the following conclusions can be drawn.  
1. The addition of fly ash-steel slag geopolymer as an admixture to loess has been found to effectively enhance the mechanical properties of the solidified soil and improve its internal structure. After a curing period of 28 days, the largest cohesion value of the solidified soil, reaching 81.09 kPa, is achieved with the addition of 20% geopolymer, which is 75.32% higher than that of plain soil. The internal friction angle is also increased to 31.12\({}^{\circ}\), surpassing that of plain soil by 62.08%. Furthermore, the unconfined compressive strength of the consolidated soil is enhanced to 570.86 kPa, which is 236% higher than that of the plain soil. Incorporating 20% geopolymer into the stabilized soil not only effectively improves its internal friction angle and cohesion but also aligns with the principles of green environmental protection and economic rationality.
2. Compared to remolded loess, the hydration of geopolymer becomes better with an increase in curing age. This leads to an effective reduction in the disintegration of solidified soil. For instance, when the geopolymer content is 20%, the solidified soil shows minimal disintegration in water even after 300 min. In scenarios involving rainfall and water accumulation, the addition of geopolymers can effectively decrease the likelihood of loess collapse, thereby reducing the occurrence of engineering accidents.
3. The analysis of XRD composition and SEM structure reveals that under the alkaline activation condition of a water glass solution, steel slag and fly ash exhibit synergistic effects. Steel slag powder releases a significant amount of Ca\({}^{2+}\) ions, which then combine with the silicon (aluminum) oxygen tetrahedron formed by the hydration process in fly ash. This combination results in the formation of amorphous gels such as calcium silicate hydrate (C-S-H) and calcium aluminosilicate hydrate (C-A-S-H), which effectively fill the pores in loess particles. As the curing time increases, the hydration products of geopolymers become more abundant, and the gelled substances of C-S-H and C-A-S-H are more plentiful. Consequently, the geopolymer vitreous body becomes enveloped by C-S-H and C-A-S-H gelling substances, effectively filling the pores and creating a more compact microstructure. This ultimately enhances the mechanical properties of the solidified soil.  
**Author Contributions:** Conceptualization, X.T. and H.L.; methodology, H.L.; validation, X.T., H.L. and X.Z.; data curation, X.Z. and M.L.; writing--original draft preparation, H.L. and X.T.; writing--review and editing, H.L.; supervision, X.T. All authors have read and agreed to the published version of the manuscript.  
This paper received funding from project LTKY2023036-1 supported by Research on Stability and Stability Control Technology of Loess High Fill Subgrade Slope in Northwest Railway and project 11962016 supported by the National Natural Science Foundation of China.  
**Informed Consent Statement:** Not applicable.  
**Data Availability Statement:** The data presented in this study are available on request from the corresponding author.  
We extend our gratitude to [PERSON] for his invaluable assistance in conducting the experiments and providing financial support for this research.  
The authors declare no conflict of interest.