Theory of universal hysterical properties of unsaturated porous media.

Theory of capillary hysteresis is presented which yields a unique, universal, nondimensional hysteresis, independant of the soil type. The theoretical model permits prediction of the hysterical domain and the water content - capillary head relationship for any process, which includes sucessive wetting and drainage, from one measured retention curve only. The theoretical model is checked against experimental data of sand soil for which no significant effect of water blockage against air entry was observed. A reasonable agreement is found between the measured main drying curve, the measured primary scanning curve and the corresponding prediction curves. The model is very convenient for calibration and operation as a practical tool for representing capillary hysteresis. - Author