The influence of back pressure and consolidation stress on the coefficient of permeabilty of compacted soils are investigated with laboratory works using compacted decomposed granite soil and the mixture of decomposed granite soil and clayey soil. Moreover, it is compared with which method is better for the saturation of soils, the vacuum adsorption for three hours and the percolation of water for seven days. From these experiments, the following results are obtained.
(1) The vacuum adsorption is better method for the saturation of soils than the percolation of water.
(2) The application of back pressure u_b =1.0 kgf/<cm>^^^2 is very effective method for saturation of soils. In this case, initial method of saturation is scarcely siginficant for the coefficient of permeability.
(3) The decrement of permeability of soils wet side of W_<opt> by consolidation is greater than that of soils dry side of W_<opt>.
(4) The properties of permeability of mixed soil is not similar to that of sandy soil or clayey soil.