Experimental Study on Sandy Loam’s Soil Water Retention Curves Through Different Wetting Methods

Understanding the soil’s water retention characteristics is crucial to monitoring and managing the earthwork infrastructures, especially during wetting induced by extreme rainfall. The adsorption of water (hydraulic wetting) and compression (mechanical wetting) of the soil skeleton can result in a higher degree of saturation (S_r). This study investigated the water retention characteristics of sandy loam wetted by two different wetting methods. Data were obtained from a one-dimensional compression apparatus for unsaturated soil. Stress-controlled and suction-controlled tests were conducted. The degree of saturation (S_r), matric suction (s), and void ratio (e) were simultaneously measured. The soil water retention curves (SWRCs), compressibility, and the e-s-S_r relationship were analysed. Finally, a typical physical model of e-s-S_r was employed to fit and analyse measured data. The results indicate that the void ratio is essential in determining the soil’s water retention curves. Denser soil performs better water retention capability. Due to suction-induced softening, the yield stress significantly decreases with lower matric suction. During the suction-controlled compression tests, the S_r slightly increases but is limited by the soil’s compressibility. The fitting results of Hu’s model indicated the dependence of the SWRC on the wetting method. It is necessary to consider the wetting paths in hydromechanical modelling for unsaturated soils.