Soil–Water Characteristic Curve of Gypseous Soil

The soil–water characteristic curve (SWCC), also known as soil–water retention curve, is a key tool in assessing the behavior and properties of unsaturated soil. The SWCC of gypseous soil with 0, 5, 15 and 25 % gypsum content was determined, using tensiometric plate, osmotic membrane and vapour equilibrium techniques, with suction pressures ranging between 10 and 1,000,000 kPa. The effect of two compaction efforts, standard and modified, was examined on the SWCC of soil samples. The water-holding capacity of soil samples increased with increasing gypsum content and applied compaction effort. Mercury porosimetry tests and scanning electron microscope images revealed that compaction and the presence of gypsum increased the number of capillary pores. These changes in the pore size distribution of soil samples induced modifications in the volumetric water content at air-entry value of the tested samples. All experimental SWCC data were fitted using the Fredlund and Xing (Can Geotech J 31(4):521–532, 1994) and Van Genuchten (Soil Sci Soc Am J 44:892–898, 1980) models. Results showed that a high coefficient of determination (R²) can be achieved by using both models to fit the experimental results of gypseous soil SWCC.