# Influence of Xanthan Gum-Based Soil Conditioners on the Geotechnical Properties of Soils
## 5 Conclusions
Regardless of the soil type, its treatment with a high dosage of SC_R and SC_ZZC resulted in similar drained shear strengths, while mixtures of soil and a high dosage of SC_CG exhibited slightly higher friction angles. This difference can be attributed to the composition of the filler in the SC_CG. Unlike the fillers in SC_R and SC_ZZC, which have an average fiber length of 200-400 \(\upmu\)m, the filler in SC_CG contains fibers with an average length of 1400 \(\upmu\)m.
5. In general, the addition of soil conditioners (SCs) decreases the saturated hydraulic conductivity of the investigated soils, regardless of the soil type. Although untreated soils exhibit significantly different saturated hydraulic conductivities, the addition of a high dosage of SCs to all tested soils leads to similar saturated hydraulic conductivities. This is attributed to pore clogging caused by the swelling of the SCs. Since the type of SCs was not identified as an influential parameter, it can be concluded that the fillers in the used SCs have no significant effect on the saturated hydraulic conductivity of treated soils. 6. The saturated hydraulic conductivity of mixtures is higher at \(\sigma_{v}t=25\) kPa than at \(\sigma_{v}t=50\) kPa, except for soil S3 with a high dosage of SCs. This aligns with the hydraulic behavior of untreated soils. The newly developed XG-based SCs exhibited favorable effects on soils in terms of water absorption and water retention capacity. Their presence could prove beneficial for retaining water and directly mitigating the consequences of extreme climatic events, such as droughts, floods, etc. However, the findings indicate that in saturated mixtures, the XG's behavior dominates, while the variation in the filler types within the SCs has only a minor effect on the strength, stiffness, or hydraulic conductivity of the treated soils. While SCs can be highly beneficial in a controlled environment (with regulated water inflow and/or controlled water content), special consideration should be taken when applying SCs in a natural environment. In natural environments, treated soils undergo a cyclic process of rainfall infiltration, evaporation, freezing, and thawing. Consequently, it is essential to systematically investigate the cyclic behavior of treated soils at various water contents and assess their durability in the future. The impact of SCs on the strength and stiffness of the soil layer could be negligible in the case of their use locally in planting holes for trees in small amounts (<1.7% per dry soil mass). In the case of applications on large areas with different thicknesses and inclinations of the treated soil layer, further attempts should be made to overcome or at least mitigate the negative impact of the SCs on the strength and stiffness of soils treated with SCs. Despitethe fact that a positive impact of the filler's fiber length was indicated only by the drained shear strength, it is believed that fillers with longer fibers can be a promising component of the SCs. This could counteract the negative effects of XG on soil strength, stiffness, and compressibility. By following this approach, it would be possible to develop a sustainable SC that not only positively influences soil water retention ability but also enhances the geotechnical properties of forest soil susceptible to erosion and slope instabilities. In view of possible future scale-up, it is necessary to consider the economic feasibility of these products. In particular, the price of Xanthan gum makes the largest contribution to the cost assessment. Additionally, the XG used in this work has food-grade quality with very high purity, which is not necessary for soil treatment applications; thus, the price of this biopolymer is expected to be significantly lower if widely applied in these sectors and purchased at an industrial scale, also considering the fact that in recent years its price decreased from 250 to 28 $/kg.