Stabilization of Expansive Soils Using Waste Plastic Fibers for Pavement Subgrades

Expansive soils pose significant challenges in flexible pavement construction due to their high shrink–swell potential and low bearing strength. To overcome these issues sustainably, this study investigates the stabilization of expansive soil using waste plastic fibers derived from discarded PET bottles. Four fiber contents—0.5%, 1.0%, 1.5%, and 2.0% by dry weight of soil—were examined to evaluate their influence on subgrade behaviour. Laboratory tests, including the Standard Proctor Test, California Bearing Ratio (CBR), and Unconfined Compressive Strength (UCS), were performed to determine changes in Maximum Dry Density (MDD), Optimum Moisture Content (OMC), and strength characteristics. Results revealed that the inclusion of plastic fibers significantly enhanced the soil’s mechanical properties. Both CBR and UCS values increased with fiber addition up to an optimum level, after which a minor reduction was observed. The strength improvement was mainly due to the random distribution of fibers, which provided effective interlocking, restricted crack development, and improved load transfer within the soil matrix. Overall, the use of PET waste fibers offers a sustainable, low-cost, and eco-friendly approach to stabilizing expansive soils, contributing to improved subgrade performance and environmental conservation.