Enhancing Sand–Geotextile Interface Strength: Effects of Polyurethane, Polyvinyl Alcohol, and Cement Slurry

Abstract Geotextiles are widely used in geotechnical engineering to reinforce soil and enhance the stability of various structures. This study investigates the effectiveness of different treatments in improving the sand–geotextile interface. A series of direct shear tests were conducted on the sand–woven geotextile interface to evaluate three treatment methods: (1) cement slurry (CS)-treated geotextile, (2) polyvinyl alcohol (PVA)-treated geotextile, and (3) polyurethane foam adhesive (PFA)-treated geotextile. Various parameters, including binder dosage, curing time, moisture content, and geotextile type, were considered to assess their impact on mobilized shear strength at the interface. The results demonstrate that these treatment methods significantly improved the interaction between sand and geotextiles, with the PFA treatment proving to be the most effective. PFA-treated geotextiles exhibited the highest mobilized shear strength in a short time, creating adhesion at the interface—an effect not observed in the PVA and CS treatments—while also enhancing the friction angle. For a given binder dosage and curing time, the PFA treatment resulted in significantly higher mobilized shear strength compared with the PVA and CS treatments, with CS yielding the lowest values. The mobilized shear strength of the PFA-treated interface was approximately 80% to 290% higher than that of the other treatments, depending on curing time and normal stress. Adhesion at the interface increased significantly by approximately 77% for the PFA treatment when the curing time was extended from 1 to 28 days, whereas curing time had a minimal effect on the friction angle. The influence of moisture content on mobilized shear strength was complex and highly dependent on the treatment method. Additionally, the effect of geotextile type in the PFA treatment was primarily significant at low PFA content. These findings highlight the potential of PFA treatment as a promising technique for enhancing geotextile performance in geotechnical applications.