Improving the bearing capacity of helical tapered piles using gum injection in FCV

Traditional cement-based grouting, widely used to restore soil resistance around piles, poses serious environmental concerns due to its high CO₂ emissions. To address this issue, this study introduces natural gum biopolymers as sustainable alternatives for pile grouting. For the first time, Persian and Arabic gums, both hydrocolloid biopolymers, were applied to improve the performance of tapered helical piles installed in poorly graded sand. Direct shear tests were conducted using a Taguchi experimental design, varying gum type, content, and curing time. The analysis revealed that Persian gum provided superior improvements in cohesion and internal friction angle compared to Arabic gum. Based on these results, Persian gum was selected for pile load tests. Axial loading experiments were then performed in the Frustum Confining Vessel (FCV) on tapered helical piles with different helix-to-diameter ratios. The results showed that gum injection increased both the ultimate bearing capacity and initial stiffness of tapered helical piles. Among the investigated configurations, the pile with closer helix spacing (λ = 1.5) exhibited the highest load-bearing performance due to enhanced interaction between adjacent helices and the surrounding soil. SEM observations confirmed that gums improved soil microstructure by forming hydrocolloid bridges between sand particles and increasing interparticle friction. Overall, the study demonstrates that natural gums can serve as effective, eco-friendly substitutes for cement, significantly enhancing pile performance.