The test and fitting analysis of Hunan clay soil–water characteristic curve in full suction range

The soil–water characteristic curve plays a key role in the study of unsaturated soils, which is the basis of unsaturated soil theory. In the paper, three different test methods, including the pressure plate test, filter paper test, and vapor equilibrium test, are used to measure the soil–water characteristic curves in the full suction range of Hunan clay samples with different initial dry densities, and the Fredlund-xing (FX) model, Van Genuchten (VG) model, and Gardner model were used to fit and analyze the test data. The effect of initial dry density on soil–water characteristic curves in the full suction range is investigated, and the differences in the effect of different models on the fitting of soil–water characteristic curves in the full suction range are analyzed, and the feasibility of obtaining soil–water characteristic curves in the full suction range based on finite experimental data is discussed. The results show that the lower the initial dry density, the greater the volumetric water content of the soil sample in the lower suction range. In the medium suction range, the lower the initial dry density, the lower the volumetric water content of the soil sample. In the high suction range, the initial dry density has little effect on the soil–water characteristic curve. The FX model provides a better fit than the VG and Gardner models. The prediction of soil–water characteristic curves for the full suction range based on finite data depends on the selection of the model and the prediction range, and the FX model’s predictions are the closest to the measured values.