Abstract:Through some experiments on the loess specimens with the prepared moisture and dry density,the characteristics of permeability for water and air phases in unsaturated soil are revealed using an apparatus for measuring water-air movement,and the mechanism of water-air movement and relationship between several measuring parameters are presented. The results indicate that air coefficients of permeability of several dry density soils experience a uniform tendency after adding a certain amount of water to the specimen with certain water content. At first,air coefficients of permeability cut down to rock bottom rapidly;then,they grow slowly;finally,the coefficients reach to constant. The time needed to reach a new stable state of permeability of pore water depends primarily on dry density and water content. Air and water coefficient of permeability will reduce with dry density increase. In addition,coefficient of permeability is not significantly influenced by the wetting path in high degree of saturation zone,while the influence is obvious in low degree of saturation.