In environmental geotechnics, transport phenomena in unsaturated soils significantly depends on the degree of saturation, because many substances are dissolved in pore water and get distributed in soil by advection with the convective flow of pore water or diffusion in the pore water itself, although there is no convective flow. By reducing the amount of pore water, this transportation path becomes less effective. Therefore, identification of key parameters which affect the soil water characteristic curve (SWCC) is an important issue in unsaturated soil mechanics for analyses of any geo-environmental problems. Although broad studies have been done on unsaturated soil behavior, but there is still no unified model which can be able to simulate soil water characteristic curve, accurately. During past decades, several mathematical functions have been proposed to model the SWCC and because of various key parameters which affect the SWCC, the proposed models are not so comprehensive. Therefore, the curves obtained from conventional tests often cannot be directly applied in practice, and the mathematical expressions from one condition cannot be used to simulate another situation. The effects of initial void ratio, initial water content, stress condition and high suction were studied in this work revealing that water content and stress state are more important than the other factors, but their influences tend to decrease when suction increases.
