An industrial by-product known as fly ash is produced when coal is burned for electricity production and is considered an environmental pollutant. To reduce environmental pollution, a comprehensive fly ash utilisation programme must be implemented, 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 use as structural fill, particularly on clay soils, when building highways and embankments. A lot of research has been done 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 concentrated on the effects of fly ash (FA) combined with clay soil. Through a series of experimental experiments, it can be said that fly ash generally increased soil stability, particularly in terms of CBR values, soil permeability, and decreased the possibility of volumetric soil changes. This is because of the size and shape of the particles, and because the volumetric dilatation of the ground has decreased over the treated period as well. The behaviour modification of the hardened soil persists since the additions are not biodegradable.