# Influence of Xanthan Gum-Based Soil Conditioners on the Geotechnical Properties of Soils
## 4 Results and Discussion
### Compressibility  
In Figure 6, the compressibility curves are shown as the relationship between the specimens' vertical strain and effective vertical stress. The compressibility curves obtained on two parallel specimens from the same untreated soil or mixture are comparable. To  
Figure 4: Liquid limit of untreated soils and mixtures with low (L) and high (H) dosages of SC_R (* represents the identification number of the untreated soil).  
Figure 5: Average water absorption of specimens from untreated soils and mixtures after 24 h (* represents the identification number of the untreated soil).  
ensure clarity and avoid information overload in the diagrams, only one test per untreated soil or mixture is presented in Figure 6.  
Despite a comparable initial void ratio between the specimens from the untreated soil and its mixtures, the compressibility curves of mixtures are shifted above the compressibility curves of untreated soils. This is the result of the free swelling of specimens from mixtures after soaking at the beginning of the test (\(\sigma_{\mathrm{v}}{{}^{\prime}}\) = 4.5 kPa). Soaked specimens of untreated soils S1, S2, and S3 did not swell. As previously demonstrated, the observed swelling of specimens from mixtures is attributed to the soil conditioners (SCs), which enhance the water absorption capacity of the soil. The swelling depends on the amount of the SC. The compressibility curves in Figure 6 illustrate that the low dosage of SC_R yields smaller swellings compared to the high dosage. The statistically significant difference (\(\alpha\) = 0.05) between specimens with low and high dosages of SC_R was also confirmed by the statistical analysis (ANOVA). It was performed on the oedometer moduli calculated for all the specimens at the same loading stage. On the other hand, the analysis showed that the influence of the type of SC is not statistically significant. No considerable swelling was observed during unloading, even at \(\sigma_{\mathrm{v}}{{}^{\prime}}\) = 4.5 kPa.  
Figure 7 (left) illustrates the time-dependent swelling of a 19.3-millimeter-high specimen from untreated soil S1 and its mixtures. The specimen is held in a rigid confining ring (Figure 7, right), which restricts lateral displacement but permits vertical swelling or compression. The measurements of the time-dependent swelling were conducted on all specimens after soaking at the first loading stage of 4.5 kPa. The results are presented only for untreated soil S1 and its mixtures. The swelling magnitude was comparable for untreated soils S2 and S3 and their mixtures. The water intake and swelling of the mixtures do not happen instantly, as was also observed during the water absorption investigation. Thus, the specimens were left to swell for approx. 2 days.  
Figure 6: Compressibility curves for untreated soils and mixtures (* represents the identification number of the untreated soil).  
Figure 7: Swelling process (\(\sigma_{\mathrm{v}}{{}^{\prime}}\) = 4.5 kPa) of untreated soil S1 and its mixtures (**left**) and specimen S1+SC_ZZC H after investigation (**right**).