Abstract
In this paper the property of free swelling of artificially crushed Tertiary (Kobe, Tsuyama and Mizunami group) mudstone is discussed. The degrees of free swelling depend on the the content of active clay minerals, such as montmorillonite and vermiculite, and the water contents are decided with pF value which is determined by soil suction, i.e. The results show that the degrees of free swelling are in proportion to the content of montmorillonite minerals in a soil and the water contents at a certain soil suction except Mizunami group mudstones.