This study explores the sustainable stabilization of clayey soils using fly ash, biochar, and polypropylene fibers to enhance geotechnical properties and mitigate heavy metal leaching. Laboratory experiments were conducted to evaluate the effects of varying proportions of biochar and fly ash on the strength and contaminant transport behavior of chemically stabilized clayey soils. Tests included Unconfined Compression Strength (UCS) after a 7-day curing period, and Scanning Electron Microscopy (SEM) to analyze microstructural interactions. Results indicated that fly ash significantly improved soil strength but introduced heavy metal leaching risks (e.g., Ba, B, Cu, Zn, Pb, Cd), potentially contaminating groundwater. Coconut husk biochar effectively reduced metal leaching but compromised soil strength. To overcome this limitation, polypropylene fibers were added, achieving a balance between strength enhancement and environmental safety. The study demonstrates the potential of combining fly ash, biochar, and fibers to develop stabilized soils with superior strength and reduced contaminant transport.