8Fredlund D G, Xing A Q. Equations for the soil-water char- acteristic curve[J]. Canadian Geotechnical Journal, 1994, 31 (4) : 521-532.
9Van Genuchten M T. A closed-form equation for predicting the hydraulic conductivity of unsaturated soils [ J ]. Science Society of America Journal, 1980,44(5) :892-898.