Abstract: The measurement and prediction of permeability coefficient of unsaturated soils with different initial void ratios are the basis of seepage analysis and hydro-mechanical coupling study of unsaturated soils, so corresponding work has great significance. As an example, Hunan red clay was chosen to prepare remoulded samples of five different initial void ratios by using jack. Then, the soil-water characteristic curve was measured by using pressure plate apparatus. Afterward, the saturated permeability coefficient was measured by variable head method, while the unsaturated permeability coefficients with different initial void ratios were obtained by instantaneous profile method using a self-made plexiglass barrel device. CCG (Childs and Collis-George) correction model and Tao-Kong model were selected to predict the unsaturated permeability coefficients, and their effectiveness was demonstrated through comparing the prediction values with the measured values. On the basis of experimental results and model prediction values, the influence of initial void ratio on unsaturated (relative) permeability coefficient was examined. The results show that the permeability coefficient of unsaturated Hunan clay decreases with the increase of matric suction in a double logarithmic coordinate, which presents a larger slope in low matric suction stage within 100 kPa while a smaller slope in high suction stage above 100 kPa. The predictions of Tao-Kong model are in good agreement with the measured values, yet great predicted errors exist in the results by the CCG model. For the suction stage larger than air entry value, the initial void ratio has little influence on the unsaturated permeability coefficient and has a greater influence on the unsaturated relative permeability coefficient. In the condition of same matric suction, a smaller initial void ratio results a greater relative permeability coefficient.

Key words: unsaturated soils, soil-water characteristic curve, instantaneous profile method, permeability coefficient