A HYSTERESIS MODEL OF SOIL WATER RETENTION CURVES BASED ON BOUNDING SURFACE CONCEPT

This paper presents a hysteresis model of soil water retention curves based on bounding surface concept. In the bounding surface concept, the plastic modulus is defined as a function of the distance between a current stress point and the conjugated stress point on the bounding surface. We adopt the similar idea that the slopes c (= -partial derivative S-r/partial derivative S) of soil water retention curves are defined as a function of the normalized distance between a current point and the conjugated points on main curves (main drying and wetting curves). The modeling of main curves was conducted by Tangential model proposed by the author. Tangential model insures the continuity of slopes of soil water retention curves. The model may well trace the soil water retention curves as if pore water pressures are both positive and negative. The model needs not to identify the parameters. Only three points are selected and the values of degree of saturation S,, suctions and slope c at the points are input. Soil water retention curves for three samples with cycles of drying and wetting were simulated using the model. The simulation results showed good agreements with the experimental ones.