Abstract: Osmotic technique is an important method for measuring the matrix suction of unsaturated soil. It is very important to control the osmotic time, which is one of the key points to obtain the accurate measurement result. Based on the finite element numerical analysis software SEEP/W, we set up a numerical model of osmotic technique to analyze water movement during the osmotic process. Then, we analyzed the influences of the suction of solution, the hydraulic properties of soil sample, the initial gravity moisture content, the initial dry density and the size of soil sample on equilibrium time of the osmotic technique for unsaturated clay in the process of humidification. The results show that with the increase of osmotic time, the difference of suction between the solution and the soil sample will decrease and then the osmotic process will become slower. Soil samples should not be too large. For small samples, the equilibrium time for the osmotic technique is about 1.5-8.0 days in most cases. The equilibrium time increases greatly when the suction of solution is high or the saturated hydraulic conductivity of soil sample is low. The equilibrium time decreases with the increase of the fitting parameters (a, n) for soil-water characteristic curve, the saturated hydraulic conductivity, the initial moisture content and the initial dry density. On the contrary, the equilibrium time increases with the increase of saturated volumetric moisture content.

Key words: osmotic technique, matrix suction, clay, equilibrium time, influence factors