A retention curve prediction for unsaturated clay soils

In order to obtain the retention curve of unsaturated soil which is defined as the relationship between water content and suction, numerous laboratory tests have been done for many soils with different clay contents. The laboratory tests concern different types of soils; the swelling and not swelling clays (natural clay with high silt content and the bentonite clay). Two complementary experimental ways are conducted. The first which leads to measure suction is based on the filter paper method. The second with the dessicator allows to impose a high suction values. The paper discusses the theoretical approaches for the grain-size distribution and water retention curve's relation. It discusses also their correlations according to each type of tested soil. The experimental data are used to validate the theoretical model selected in the study. The influence of the different parameters used by the model is also studied. All the parameters required to run the model can be obtained by performing independent, common laboratory tests and are related to the physical parameters like the initial dry density and the initial void ratio. After some numerical tests, the direct procedure to obtain the soil-water characteristic curve is improved.