Enhancing Geomechanical Properties of Clayey Soils Through the Combined Application of Polypropylene Fibers and Eggshell Powder

Soil stabilization is an effective method for improving the mechanical behavior of clayey soils in construction projects. This study investigated a sustainable approach using eggshell powder (ESP) and polypropylene fibers (PPF) as stabilizing additives. ESP was used at 0%, 5%, 10%, 15%, and 20%, and PPF at 0%, 0.5%, 1%, 1.5%, and 2% by dry weight of the soil. The mixtures were evaluated through compaction, unconfined compressive strength (UCS), and ultrasonic pulse velocity (UPV) tests after 28 days of curing under laboratory conditions. The results indicated that the combination of 10% ESP and 1% PPF achieved the best performance, with a UCS of 346.6 kPa, modulus of elasticity (E50) of 3911 kPa, and UPV of 1126 m/s. This mixture also resulted in a reduced optimum moisture content (ωopt) of 18.3% and a maximum dry unit weight (γdmax) of 17.3 kN/m3. The addition of PPF enhanced the ductility and energy absorption capacity of the soil. Statistical analysis using analysis of variance (ANOVA) confirmed the significant influence of both additives on UCS and UPV, with ESP exerting a dominant effect, particularly on UPV. ANOVA outperformed Multiple Linear Regression (MLR) and nonlinear regression models in predictive reliability, while the second-order nonlinear model offered near-optimal accuracy with fewer parameters than higher-order alternatives. This research introduced a novel and eco-friendly method for stabilizing clayey soils by combining two readily available waste materials. The findings offered a cost-effective and practical solution for improving soil performance in geotechnical applications while contributing to environmental sustainability.