For red mudstone cannot be used as the subgrade filler directly, the red mudstone filler on an expressway was improved by using lime, fly ash and cement as a modifier respectively. The optimum moisture content, CBR value, unconfined compressive strength, resistance to disintegration and water stability test as well as electron microscope scanning were carried out on the 15 modified samples. The results show that the effect of fly ash on the optimal water content is larger than that of lime. The sequence of improvement effect on unconfined compressive strength and resistance to disintegration among cement, lime and fly ash is cement ＞ lime ＞ fly ash. Under the same modifier ratio, the cement is the strongest, lime is inferior and the fly ash is the worst on the overall effect. When the lime ratio is 7 ％, the unconfined compressive strength is the largest, i. e., the best ratio. The modification of micro structure shows that the modified agent is achieved the purpose of improving the stability of subgrade filler by hydration reaction with the combined water and free water through ion exchange with the clay minerals in the red mudstone.%分别选用石灰、粉煤灰、水泥作为改良剂,对某高速公路红层泥岩填料进行改良.对改良后的15组试样进行最优含水率、CBR 值、无侧限抗压强度、耐崩解性、水稳定性的测试,并作电子显微镜扫描.结果表明: 粉煤灰对最优含水率影响较大,石灰次之; 水泥、石灰、粉煤灰对无侧限抗压强度、耐崩解性的改善整体排序为水泥＞ 石灰＞ 粉煤灰; 相同配比情况下,水泥对填料的整体改善作用最好,石灰次之,当石灰掺入比为7 ％ 时无侧限抗压强度最大,即为最优配比.
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