عنوان مقاله [English]
Soil-water retention curve describes the relationship between soil suction and soil water content; it has a wide application from predication of unsaturated shear strength to transient two-phase flow and stability analyses. All physically possible set of retention curves for a soil with specified state parameters are bounded by the two main drying and wetting curves corresponding to the upper and lower bound, respectively. As a result, the characterization of these two boundary curves as well as the hydraulic hysteresis is of great importance in problems related to the both geo-environmental and hydro-geological fields of research. The reason is that recent investigations have revealed that the hysteresis phenomenon can significantly affect the stability of natural slopes and hence the consideration of only one hydraulic path may not necessarily result in the worst case scenario. However, direct measurement of the soil-water retention curve requires advanced laboratory equipment and high expertise. In addition, the experimental output has a discrete nature and is usually limited to low suction ranges compared with the theoretical full range. In other words, the direct incorporation of experimental data to numerical flow and stability analysis becomes impossible, so continuous mathematical modelling is inevitable. Consequently, there has always been great interest in the analytical modeling of the soil-water retention curves. On the one hand, no thorough study can be found in the literature so far to collect and revisit the pros and cons of various analytical modeling approaches for simulation of this key hydro-mechanical feature. Therefore, the main objective of current study is to provide a comprehensive review of all available modelling philosophies with emphasizing the capabilities and fundamental limitations of each approach. The paper is especially distinctive in classifying all current approaches under seven categories and in providing insight into the general framework of each one. Eventually, a discussion, highlighting the shortcomings and essential modelling needs, is provided to shed light on potential research directions in future.