ABSTRACT
The soil water characteristic curve (SWCC) is a continuous sigmoid function that correlates the presence of water with suction. This curve describes important features of soils when their saturation state is altered. Soils remain fully saturated with increasing suction up to the air entry value (AEV) when air starts to enter into pore spaces under capillarity. Thereafter, soils continuously lose water with increasing suction until the residual state. The remaining water is difficult to force out and complete soil desiccation requires a suction of 106 kPa. The curve comprises of three straightline portions: a horizontal line from saturation to the AEV; a steep downward slope from the AEV to the residual state; and a flat downward slope from the residual state to the completely dry state. The curve shape is affected by the following soil properties: (i) grain sizes and soil microstructure that influences pore tortuousity; (ii) dry unit weight that is related to the total void space in a soil; and (iii) clay mineral types and amounts that dictate the amount of adsorbed water.
