Abstract: Sinking of DCM columns at their tops occurs in some highways. In order to explain the reason of the sinking of DCM columns, pore water pressure cells and earth pressure cells are installed in the soils among DCM columns at different depths. A method to predict the sinking of columns is presented according to the difference between the earth pressure and the excess pore water pressure. The thixotropy of saturated silty soils due to the construction of DCM columns is studied using the results of static cone penetration tests and in-situ and laboratory results of soil mechanics. The strength of saturated silty soils increases with time after the construction of DCM columns.