## 5 Conclusions  
This study employs xanthan gum and calcium lignosulfonate as stabilizers to enhance gravelly soil. The mechanical properties and strength parameters of the stabilized gravelly soil were analyzed through the conduct of unconfined compressive strength tests and conventional triaxial compression tests. Additionally, scanning electron microscopy (SEM) was used to investigate the stabilization mechanisms of both additives. The following principal conclusions are drawn:  
1. As the dosage of xanthan gum is increased, the unconfined compressive strength, peak deviator stress, and the cohesion and internal friction angle of the soil exhibit a nearly linear increase. In contrast, for calcium lignosulfonate-stabilized soil, these parameters initially increase and then decrease. The optimal compressive and shear strength effects are observed at a dosage of 4%.
2. At equivalent dosages, xanthan gum-stabilized gravelly soil displays enhanced performance in comparison to calcium lignosulfonate-stabilized soil. Moreover, at elevated confining pressures, the cementing impact of xanthan gum and calcium lignosulfonate on gravelly soil is comparatively diminished in relation to the strength imparted by the confining pressure, suggesting that the influence of dosage on the shear strength of gravelly soil is attenuated.
3. The formation of a binder in the gravelly soil by the hydration of xanthan gum can result in the creation of a \"bridging\" structure with soil particles, thereby enhancing the tensile strength of the soil. Furthermore, the binder fills the micropores between the soil particles, thereby reducing stress concentration and increasing the overall strength of the gravelly soil matrix.
4. Calcium lignosulfonate enhances the structural stability of gravelly soil and increases its strength through mechanisms such as ion exchange, adsorption and encapsulation of soil particles, filling of micropores between particles, and cementation.  
Conceptualization, C.P.; Methodology, C.P. and J.Z.; Software, J.Z.; Validation, J.Z. and H.Z.; Formal analysis, J.Z.; Investigation, C.P. and H.Z.; Resources, C.P.; Data curation, J.B.; Writing--original draft, J.Z.; Writing--review & editing, C.P. and D.W.; Visualization, D.W.; Supervision, C.P. and D.W.; Project administration, C.P.; Funding acquisition, C.P. All authors have read and agreed to the published version of the manuscript.  
The writers gratefully acknowledge the financial support from the Open Fund of the Key Laboratory of Earth and Rock Dam Damage Mechanism and Prevention and Control Technology, Ministry of Water Resources, China (No. YK319008), the National Natural Science Foundation of China (No. 52079098), and National Natural Science Foundation of China Youth Funded Projects (No. 51708273). This work was supported by the Youth Science Fund (A-class) of Hunan Natural  
Figure 12: Mechanism diagram for lignin-cured gravel soil.  
Science Foundation (2025 JJ20049) and Natural Science Fund for Distinguished Young Scholars of Hubei Province (No. 2024 AFA051).  
**Institutional Review Board Statement:** Not applicable.  
**Informed Consent Statement:** Not applicable.  
**Data Availability Statement:** The raw data provided in the study is included in the article's figures and tables; for further enquiries, please contact the corresponding author.  
**Conflicts of Interest:** The authors declare no conflict of interest.