Disposed coal ash become environmental important issues and number of production is abundant, and can be considered as waste material if it is not effectively reused or recycled for other application. In engineering practice, utilization of fly ash as additive materials is limited and in small quantity while the fly ash disposal is quite high. The major aim of this paper is to stress the characterization, classification and utilization of coal ash for road application. Also, to prove of coal ash contribution in soil improvement, give benefit in engineering practice and also become as part of engineering material that is environmental friendly. Geotechnical analysis and soil-coal ash mixture characteristics involve physical, mechanical and chemical properties, including environmental aspect are presented. Result shows that effect of addition of fly ash, bottom ash and lime on physical and mechanical properties can improve the index properties of soft clay, increases strength and bearing capacity, as well as decreases swelling potential. Coal ash-soil mixture contains some heavy metal elements, but low concentration values and environmentally acceptable. Finding of the optimum utilization of coal ash as substitution material in sub base and as soil stabilization in sub grade are also discussed.