The use of biopolymers like Xanthan Gum (XG) for soil stabilization offers an eco-friendly alternative, enhancing soil properties while reducing CO₂ emissions, gaining attention in sustainable engineering. This study investigated the interaction and geotechnical improvements of clay mixed with XG and polypropylene fibers (PPF). Biopolymer was used in proportions of 1%, 3%, and 5%, while the PPF percentage was kept constant at 0.5% by weight. Additionally, the molding density was varied at 1.65 g/cm³, 1.70 g/cm³, and 1.76 g/cm³. A total of 108 specimens were prepared using two curing times (28 and 90 days), and the samples were subjected to unconfined compressive strength (UCS) tests, ultrasonic pulse velocity (UPV), and Scanning Electron Microscopy (SEM). The results demonstrate that the addition of XG and PPF in the specified proportions provides significant mechanical improvements to the stabilized soil. The curing time had a notable impact on these improvements; a curing time of 90 days resulted in strength increases of up to 37% compared to 28 days, while the maximum dry density improved this property by up to 87% compared to the minimum density. The incorporation of PPF enhanced strength by 53.93%, while stiffness increased by 63.55%. Additionally, the strength ($q_{\mathrm{u}}$) and stiffness ($G_o$) results were successfully correlated using the porosity/binder index $\eta /B_{iv}$, achieving determination coefficients (R²) greater than 0.90 and 0.80, respectively.

Artificial cementation of granular soils results in improved stabilization, increased stiffness, and greater mechanical strength. The porosity index and volumetric cement content $\left(\eta /{C_{iv}}^a\right)$ is presented as a key measure to study the evolution of different soil stabilization types. However, this index had not been previously studied or adjusted for sands in Colombia. Therefore, this study evaluates the applicability of the $\left(\eta /{C_{iv}}^a\right)$ index on unconfined compressive strength $({\mathit{q}}_{\mathit{u}}$) and stiffness ($G_o$), complemented by microstructural analysis, in four sandy soils from Luruaco (Atlántico), Lorica (Córdoba), Medellín (Antioquia), and Bogotá D.C. The soils were stabilized with Type III Portland cement in dosages of 3%, 5%, 7%, and 9%, and subjected to UCS, ultrasound, and SEM-EDS tests after a curing period of 7 days. It was found that increasing cement content results in higher ${\mathit{q}}_{\mathit{u}}$ values for the samples, and higher molding density also leads to higher ${\mathit{q}}_{\mathit{u}}$ values. Additionally, the grain size distribution influenced the adjustment of parameter “a”. In the sands from Bogotá and Lorica, with high uniformity, the value of “a” was 1.00. In contrast, mineralogy and particle shape played a predominant role in the sands from Medellín and Luruaco, where the coefficient of uniformity is higher, suggesting a possible inverse relationship between particle angularity and the value of “a”.

Artificial sand cementation improves stability, stiffness, and mechanical strength, making it a critical process in geotechnical applications. This study analyzes the capability of the porosity–water/binding agent index $(\eta C_w/B_{iv})$ to predict cemented sands’ unconfined compressive strength $(q_u)$ and stiffness $(G_o)$. Four Colombian sands, i.e., Luruaco, Medellín, Lorica, and Bogotá (stabilized with Portland cement), and were compared with three Brazilian sands: i.e., Osorio, Porto Alegre, and Rio Pardo were evaluated, stabilized with combinations of carbide lime and glass powder, using varying binder contents and a curing period of seven days subjected to ultrasonic pulse velocity (UPV) tests and unconfined compressive strength (UCS) tests. The results indicate that incorporating water content into the index significantly enhances predictive accuracy, achieving R² values above 0.94 for Colombian sands and considerably better fits for Brazilian sands than the traditional porosity/binder index. This new alternative provides an appropriate parameter for representing the small-strain stiffness and unconfined compressive strength of artificially cemented sands stabilized with various types of binders. Furthermore, the new index proved to be more effective in predicting the behavior of uniform and loose-graded sands, such as those from Bogotá and Lorica, which rely more heavily on binder volume and water content to achieve greater strength and stiffness. Lastly, the predictive model, validated against experimental results, achieved reliability indices (R²) of 0.9791 for stiffness and 0.9799 for strength prediction.

Research on sustainable alternatives to conventional soil stabilization has promoted the use of natural biopolymers as partial substitutes for cementitious binders. This study presents a mechanical and microstructural comparison between poorly graded Colombian sand stabilized with guar gum (GG) and Type III Portland cement. GG was incorporated at 0.25–1.00% with curing periods of 28 and 90 days, while cement contents ranged from 3 to 9% with 7 days of curing. A total of 108 cylindrical specimens were tested using unconfined compressive strength (UCS) and SEM–EDS analyses. Results show that both binders significantly improve soil strength, although cement exhibits a steeper strength gain due to hydration processes. GG-treated samples reached a maximum UCS of 470 kPa at 90 days, representing an increase of approximately 40% compared to 28 days and showing comparable performance to 5% cement. The porosity/binder index (η/B_iv) demonstrated a strong correlation with UCS (R² > 0.91), confirming its predictive capability. Microstructural analysis revealed the formation of C–S–H and ettringite in cement-treated samples, while GG-treated soils exhibited hydrogel bridges and the presence of pores that may influence particle bonding. Overall, the results demonstrate the technical feasibility of GG as a sustainable soil stabilization alternative.