Enhancing the mechanical and shear behavior of clay soil using lime, Nano-MgO, and recycled PET fibers: experimental and UPV-based assessment

Clay soils, due to their inherent low strength and undesirable engineering properties, usually require improvement and stabilization before use in geotechnical projects. In this study, a hybrid improvement system including lime, nano-magnesium oxide (nano-MgO), and recycled polyethylene terephthalate (PET) fibers was examined as an integrated chemical–mechanical approach for improving clay soil behavior. For this purpose, unconfined compressive strength (UCS), indirect tensile strength (ITS), direct shear, and ultrasonic pulse velocity (UPV) tests were performed on samples with various additive contents at curing times of 7, 14, 28, and 90 days. The results showed that the optimum mixture containing 10% lime, 2% nano-MgO, and 0.9% PET fibers considerably enhanced the mechanical and shear characteristics of the soil. The UPV results showed a strong and consistent relationship with the mechanical properties of the stabilized soil. This strong correlation confirms the reliability of UPV as a rapid and fully non-destructive evaluation method. Overall, the combined use of lime, nano-MgO, and PET fibers proved to be an effective strategy for improving the strength, durability, and structural integrity of clayey soils.