## 3 Results and Discussion
### Oedometer Tests  
The e-log\(\sigma^{\prime}_{\rm v}\) curves obtained from the one-dimensional compression (oedometer) tests for the five different organic matter contents are illustrated in Figure 6. Despite some scattering in terms of the evaluation of the void ratio, in qualitative terms there were some similarities in the curves; mainly:  
Figure 5: SEM images (2000X) of soil stabilized with 1% of XG for an OM content of: (**a**) 1.5%; (**b**) 7.7%.  
1. a progressive increase in the compressibility with the increase in the vertical stress. 2. The increase in the void ratio with the OM content, which agrees with the findings of [PERSON] et al. [48]. 3. The upward movement of the e-log\({}^{\prime}\)v curves after the stabilization with XG due to the hydration of the biopolymer's hydrogels, which induces an increase in the void ratio; this tendency matches with the results of [PERSON] et al. [29].  
Figure 7 highlights the effect of the OM content on the initial void ratio and on the change in the void ratio during compression (\(\Delta\)e\({}_{\text{compression}}\)) and swelling (\(\Delta\)e\({}_{\text{swelling}}\)). These results clearly show the increase in the initial void ratio after the stabilization of the soil with XG, and this effect is enhanced with the increase in the OM content. In fact, this behavior can be explained by two cumulative factors--the high ability of the organic matter to retain water, and the hydration of the hydrogels of the XG when water is present--which together potentiate a high void ratio for a stabilized soil with a high OM content. Figure 7 also demonstrates that the change in the void ratio (both in compression and swelling) increases after stabilization with XG; although, as expected, with a greater variation for the compression paths than for the swelling paths. Additionally, in the compression paths the \(\Delta\)e increases with the OM content, while in the swelling path the \(\Delta\)e is negligible in relation to the change in the OM content. Figure 8 illustrates the effect of the variation in the OM content on the compression index (Cc) and the swelling index (Cs). Naturally, the tendency observed by Cc and Cs corroborates the features described concerning the evolution of \(\Delta\)e\({}_{\text{compression}}\) and \(\Delta\)e\({}_{\text{swelling}}\) in Figure 7. Indeed, Cc increases after the stabilization of the soil and this effect is amplified for higher OM contents. Moreover, Cs is relatively unaffected by the organic matter content, increasing slightly for the stabilized soil.  
Figure 7: Oedometer tests. Effect of organic matter content on the: (**a**) initial void ratio, (**b**) variation of void ratio during compression (9.0 to 902 kPa) and swelling (902 to 1.5 kPa).  
The effect of the stabilization process and the variation in the organic matter content on the coefficient of consolidation (Cv) evaluated for the vertical stress increment between 450 and 900 kPa is presented in Figure 9. In line with other research work [39; 48; 49], the Cv of the unstabilized soil decreases with the increase in OM content, which corresponds to an increase in the primary consolidation time. This behavior is fundamentally due to the significant ability of the OM to absorb water, which induces a higher void ratio and a higher compressibility. On the other hand, the stabilization process induces a significant decrease in the Cv, which is related to the capacity of the biopolymers to retain water, due to the hydration of the hydrogels. This means that the stabilization of a soil with XG prolongs the time required to complete primary consolidation.