Abstract: The permeability is an important parameter which reflects the moisture movement in unsaturated soil. In this paper, a soil column device is designed combining instantaneous profile method and filter paper method to determine permeability function. The device includes a continuous water supply system at the upper part and a soil column composed of soil sample with a cylinder and filter paper at the lower part. During the infiltration, the mass of soil samples and filter papers are measured to determine the water content profile and hydraulic head profile. Then the soil-water characteristic curve and permeability curve are calculated by these data. The Malan loess and the first layer of paleosol from Zhengning, Gansu province are tested. The results show that the method covers a wide range of suction from 1 to 105 kPa, and permeability coefficient range of 10?5?10?13 m/s. This method is simple, inexpensive, and available for both intact and remolded soil. Moreover, several common statistical permeability models including Childs & Collis-Geroge model, Fredlund model, van Genuchten model, and Priesack & Durnerare model are used to predict the permeability curve of the two soils. The results show that the predicted results are consistent with the measured results in low suction range, while they are not in high suction range.

Key words: unsaturated soil, permeability curve, filter paper method, instantaneous profile method, statistical models