This study explores a novel stabilization technique combining Persian gum (PG), an eco-friendly biopolymer, and glass fiber (GF) to enhance the strength and durability of fine-grained soils under freeze-thaw (F-T) cycles. Specimens were prepared at maximum dry density (MDD) with varying PG and GF contents, cured for 0, 7, or 14 days, and subjected to 0, 5, 7, or 10 F-T cycles. Tests included Standard Proctor compaction, Scanning Electron Microscopy (SEM), Unconfined Compressive Strength (UCS), and Direct Shear (DS). Results demonstrated that GF significantly improved durability, ductility, and strength by enhancing interparticle interaction and friction angle. The results indicated that at an optimum GF content of 1%, UCS and E-5(0) increased by up to 35%. Also, after 10 F-T cycles, UCS decreased by 46% for untreated soil and 36% for treated soil. PG enhanced cohesion through interparticle bonding, which was curing-time-dependent. Specimens with 2.5% PG (optimum content) showed a 133% UCS increase after 14 days of curing but a 9% reduction after 5 F-T cycles, with 70% of total UCS loss occurring in the first 5 cycles. The tests indicated that formation of large and stable soil-PG-GF matrix with improved rigidity, strength, and F-T resistance. The results demonstrated that the suggested soil stabilization method, which utilizes low-cost, eco-friendly materials, was effective.

Construction on silty sand soils on the riverbank, which are typically loose, can cause geotechnical problems. Therefore, it is essential to improve their short-term and long-term behavior. Sustainable development encourages geotechnical engineers to use eco-friendly materials in soil improvement. This study investigates the effect of Kenaf fibers (KF) and Persian gum (PG) biopolymer on stabilizing silty sand with low shear strength. Short-term behavior was assessed using standard Proctor compaction, unconfined compressive strength (UCS), and indirect tensile strength (ITS) tests, while long-term performance was evaluated through the direct shear test. The effects of initial moisture content, PG and KF percentages, curing time, and temperature on mechanical properties were analyzed. Additionally, ultrasonic pulse velocity (UPV) and scanning electron microscopy (SEM) tests examined the microstructure of the improved soil. Results showed that the optimum PG and KF contents were 2.5 % and 1 % by soil weight, respectively. The UCS of samples containing these additives increased by 75 % compared to unstabilized soil. The highest UCS was achieved at 50 degrees C, with 5.1 times increase, while at 110 degrees C, it decreased by 67 % due to thermal degradation. Direct shear tests confirmed that KF reinforcement consistently improved shear strength. The UPV showed a strong correlation with UCS, supporting its use as a non-destructive evaluation method. Also, SEM analysis showed that PG enhanced particle bonding, while KF reinforcement created a denser and more interconnected soil structure. This study highlights the effectiveness of PG and KF as sustainable alternatives for soil stabilization, showing improved soil properties and environmental issues.

This study used Persian gum (PG) as a sustainable anionic hydrocolloid to alternative traditional stabilizers to stabilize this soil. For this purpose, unconfined compressive strength (UCS), ultrasonic pulse velocity (UPV), and direct shear tests were performed after freeze-thaw cycles. The results show that biopolymers can improve UCS by creating stronger bonds between soil particles and effectively reducing the adverse effects of freeze-thaw cycles compared to unstabilized clayey soil. Also, the accumulative mass loss by adding 2% of Persian gum to unstabilized clayey soil decreased by about 70% due to the adhesive property and interaction of Persian gum hydrogel with soil grains. In addition, the moisture loss is reduced with the addition of biopolymer compared to the unstabilized sample. The UPV of the samples under the freezing phase is higher than in the thawing phase. The internal friction angle and cohesion of unstabilized and stabilized clayey soil with 2% Persian gum increased and decreased under freeze-thaw cycles. Overall, the findings show that anionic hydrocolloids such as Persian gum can effectively improve the performance and durability of CH clayey soil under severe freeze-thaw conditions.

Silty sandy soils usually have low shear strength due to their non-cohesive structure, weak internal bonds, and high porosity. Environmental challenges, such as freeze-thaw (F-T) cycles, also reduce the mechanical characteristics and instability of infrastructures and structures built on these soils. Biopolymers and fibers offer a sustainable solution to improve soil strength and F-T strength. However, while much research focuses on stabilizing silty sand, fewer studies examine the combined effects of biopolymers and fibers on soil properties under F-T cycles. Additionally, the correlation between ultrasonic pulse velocity (UPV) and unconfined compressive strength (UCS) in biopolymer-stabilized and fiber-reinforced soils still needs to be explored. This study examines the stabilization of silty sand using Persian gum (PG) (0.5-3%) and kenaf fibers (KF) (0-1.5%) with lengths of 6, 12, and 18 mm at the curing times of 7, 28, and 90 days. The samples were subjected to F-T cycles (0, 1, 2, 3, 6, and 12). The results showed that the highest UCS was achieved with 2.5% PG and 1% KF (12 mm) after 28 days. After 12 F-T cycles, the UCS reductions were 41% for sample with 2.5% PG and 34% for sample 2.5% PG and 1%KF. The swelling after freezing for the 2.5% PG and 1% KF sample and the 2.5% PG sample was 4.8% and 3.45%, respectively. A correlation between UPV and UCS after various F-T cycles was suggested. The scanning electron microscopy (SEM) analysis revealed increased voids, weakened polymer bonds, and cracks after 12 F-T cycles.