An industrial by-product known as fly ash is produced when coal is burned for electricity production and is considered an environmental pollutant. A comprehensive fly ash utilisation programme must be implemented to reduce environmental pollution, including numerous factors at different levels. Fly ash's geotechnical qualities, including its specific gravity, permeability, internal angular friction, and consolidation characteristics, make it ideal for structural fill, particularly on clay soils, when building highways and embankments. Much research has been conducted on how fly ash affects soil stability. In order to determine the impact of fly ash addition on soil properties, this inquiry reviewed a few of these papers and conducted a critical assessment. This study also looked at combining fly ash and clay soil. Numerous investigations indicate that fly ash generally improves soil stability, notably when analysing CBR values and soil permeability, and reduces volumetric changes in the soil. The ground becomes compact due to particle size and form and a decrease in volumetric dilatation. Because the additives to the hardened soil do not dissolve, the soil's behaviour continues to be modified. [ABSTRACT FROM AUTHOR]