Direct measurement method and prediction formula for permeability coefficient of unsaturated soils

Various measurement methods and prediction models for the permeability coefficient of unsaturated soils are summarized. A method for measuring the permeability coefficient and a prediction model are proposed. This measurement method, based on the multistep outflow method, can measure the soil-water characteristic curve and the water content of the soil samples in real time. In this method, the increment of gas pressure potential is divided into two parts: one part overcomes the osmotic resistance and drives pore water, the other balances the surface tension of hydrostatic equilibrium conditions and converts it into matrix potential, then, the permeability coefficient can be obtained by the Darcy's law. On the other hand, the predicted model is derived based on the equilibrium equation of the water phase. Only one parameter is required, and this parameter can be more easily obtained by using the permeability tests on saturated soils with different porosity values. A number of test results in the literatures are employed to validate the proposed measurement method and predicted model, and they indicates good agreement with the experimental data.