## 1 Introduction
In terms of the coefficient of consolidation (Cv), results of the treatment of a marine soft soil [30], high plastic soil [36], and kaolinite clay [35] with XG promotes a significant reduction in the Cv; i.e., the stabilization with XG prolongs the time required to the end of the primary consolidation. Additionally, the coefficient of secondary compression of a kaolinite clay increases after the stabilization with xanthan gum [35]; 5. Increases the pH value [34] and the plasticity index [19; 26; 34], and decreases the specific gravity [34]; 6. Changes the compaction characteristics, namely, it increases the optimum moisture content and decreases the maximum dry density of a tropical residual soil [34], a dispersive soil [37], and a kaolinite clay [26]; 7. Increases the undrained shear strength of a kaolinite clay, but decreases the undrained shear strength of a montmorillonite clay [38]; 8. Decreases the cumulative variation in moisture loss and mass loss in freeze-thaw tests [36]; 9. Decreases the swelling potential of a high plastic soil [36]. Some research works indicate that the effectiveness of XG in stabilizing soils results from the contribution of two effects: (i) the aggregation of the soil particles due to the deposition of the XG in the voids; and (ii) the bonds established between the XG (hydrogen bonding) and the surfaces of the soil particles, mainly when they are electrically charged, as it occurs in clayed soils [2; 27]. These two effects justify the greater effectiveness of the XG in stabilizing clays than coarse-grained soils, since in clays, both effects are cumulative in strengthening the soil. Nevertheless, in coarse-grained soils the improvement of the mechanical properties is only due to the deposition of the XG in the porous space of the soil, inducing the generation of a network of XG fibers, similar to micro-reinforcement of the soil, as illustrated in Figure 1 for a silty sand. Some experiments with specimens of silty sand submitted to curing in humid conditions indicate that the stabilization with XG is potentiated for a curing time of 7-14 days and for an XG content of approximately 1% [29]. For a curing time of less than 3 days, a detrimental effect of the stabilization with XG was observed [29]. Although xanthan gum is a biodegradable biopolymer, which is naturally associated with a progressive loss of its properties with elapsed time, some experimental results show a high stability over time in strengthening the soils in dry environments. Indeed, the benefit of XG strengthening such soils tends to grow with curing time [23; 27; 29; 31; 37], and even in the long-term (until 730 days) no traces of biodegradability in a sand-XG mixture were observed [27]. On the other hand, the evolution over time of the permeability coefficient (in saturated conditions) did not show results totally consistent with a great stability over time. In fact, the results of [PERSON] et al. [22] reveal a decrease in the permeability coefficient of a sandy-XG mixture during the curing time, while the opposite was observed in a clayed soil [24] and a sandy soil [23]. Additionally, the results of [PERSON] et al. [25] show a decrease in the permeability coefficient of a sandy soil during the first 14 days of curing time, followed by a slight increase in the permeability coefficient for higher curing times, which may be the consequence of some biodegradability and/or some dehydration of the biopolymer's hydrogels over time [25; 32]. Some previous research has described the efficiency of the treatment of soils with xanthan gum, namely concerning the effect of several factors (such as soil type, curing time, content of XG, among others) on the strengthening, plasticity [30; 32] and the permeability coefficient.