Abstract
In order to utilize coal ashes which are Produced from thermal p ower plants as material to improve defective soil, the important factors and suitable level of addition of coal ashes to soil were found out by using statistic analysis (design of experiment and multiple regression analysis). The analytic results show that the coal ashes themselves have less strength effect, but are effective to create the environment (moisture content, pH) promoting chemical reaction in the soil. Furthermore, it has the catalytic function to promote the effect of quicklime which is main content of ashes. It is almost confirmed that the addition of ashes to soil could be more than 12%. KEYWORDS: improvement material of defective soil, surplus fly ash, quicklime, gypsum statistics technique.
