Enhancing the Strength and Resilient Behavior of Subgrade Using PET and Polypropylene Fiber

This project investigates the enhancement of clay soil for pavement subgrade design by incorporating polypropylene fiber (PPF) and polyethylene terephthalate (PET) as additives. The primary aim was to determine the optimum proportion of PPF and PET that improves the soil’s strength, compaction, and resilience. Laboratory tests, including the Standard Proctor Test, Unconfined Compressive Strength (UCC) Test, California Bearing Ratio (CBR) Test, and Resilient Modulus (Mr) determination, were conducted on soil samples with varying percentages of PPF and PET. The results showed that the optimum combination for reinforcing clay soil was 0.6% PPF and 2% PET, which significantly improved the soil’s compaction properties, compressive strength, CBR values, and resilient modulus. Specifically, the compressive strength increased from 63 to 91 kN/m2 with the optimum combination, and CBR values improved from 3.7 to 6.67% at 2.5 mm penetration. The resilient modulus also increased from 37 to 59.29 MPa. These improvements indicate that the addition of PPF and PET enhances the soil’s ability to resist deformation under traffic loads, making it more suitable for use in pavement subgrades. The findings demonstrate the effectiveness of using waste materials like PET in soil stabilization, contributing to sustainable infrastructure development.