Modeling the hysteretic behavior of the capillary pressure in partially saturated porous media: a review

In this review, the phenomenology of hysteresis is discussed, including both empirical and mathematical models, and some examples are presented. The focus lies on soil-moisture hysteresis, where the capillary pressure exhibits different values depending on the initial state of saturation. An historical overview is given of the investigation of this phenomenon, of various empirical models, and also of some mathematical approaches to soil-moisture hysteresis. All these studies are aimed at accurately fitting experimental results—not only the main hysteresis curves but also the inner hysteresis curves that occur upon re-wetting and re-drying. Finally, a comparison is made to another field in which hysteresis appears, the deformation of pseudoelastic bodies such as shape memory alloys.