(2) van Genuchten, M. T.: A closed-form equation for predicting the hydraulic conductivity of unsaturated soils, Soils Science Society of America Journal, Vol.44, PP. 892-898, 1980.
(3) Bishop, A. W.: The principle of effective stress, Publication 32, Norwegian Geotechnical Institute, Oslo, pp.1-4, 1959.
(4) Russo, D. and Bresler, E.: Field determination of soil hydraulic properties, Water Resources Research, Vol.24, pp.453- 459, 1980.