Abstract: The hydraulic parameters of unsaturated soils, including soil-water characteristic curve and permeability function, are very important to unsaturated soils. Because the traditional test method is time-consuming, one-step outflow method and dynamic multistep outflow method are proposed to get hydraulic parameters of unsaturated soils quickly; and the combined testing system is adopted to carry out the two flow tests. The results show that the differences of soil-water characteristic curves between the estimated and measured ones are small. The two methods also can avoid the problem of high-pressure gas through the water leaking in the back of the ceramic plate. The time of the one-step outflow method is shorter, but its accuracy is worse. So the dynamic multistep outflow method is superior to the one-step outflow method.

Key words: combined testing system, one-step outflow test, multistep outflow test, soil-water characteristic curve, hydraulic permeability function