Reinforcement of Silty Soil via Regenerated Fiber Polymer: A Study on Microscopic Mechanisms

Utilizing regenerated polyester fibers (RPFs) for the reinforcement of silty road bases not only enhances the soil’s engineering performance but also offers a sustainable method for repurposing waste polyester bottles. To investigate the engineering properties and microscopic behaviors of this reinforced silty soil, a series of extensive physico-mechanical tests were conducted, supplemented by Scanning Electron Microscopy (SEM) analyses. These evaluations focused on the influence of variables such as fiber content, fiber length, moisture content, and curing duration on the modified soil’s performance. The fiber content of the test was 0–1%, and the fiber length was 6–17 mm. The results indicate that curing age had a less significant impact on liquid and plastic limits than the addition of fiber, along with a marginal decline in the plasticity index over time. The rate of shrinkage in the unmodified soil was between 1.04 and 1.45 times higher than that in the fiber-reinforced soil, indicating effective shrinkage control by the fibers. However, variations in maximum dry density (ρ(dmax)) were insignificant across different fiber contents, while a slight increase was observed in the optimum moisture content (OMC) as fiber dosage increased. After a 28-day curing period, the resilient modulus and California Bearing Ratio (CBR) met highway road base design standards. A decline in unconfined compressive strength was noted when the fiber dosage exceeded 0.2%. The addition of fibers mitigated diagonal cracking and shifted the failure pattern towards a more ductile mode. This research contributes scientific insights for the broader application and promotion of silty road base improvement techniques using RPFs.