On the characterization of the shrinkage behavior and soil-water retention curves of four soils using centrifugation and their relation to the soil structure

In this study, a consistent centrifuge procedure was applied to four soils. The height shrinkage, bulk density increase, soil shrinkage curve (SSC), and soil-water retention curve (SWRC) of the soils were analyzed. Scanning electron microscopy (SEM) tests and image processing techniques were adopted to qualitatively and quantitatively investigate the microstructure of the soils with different bulk densities. The results showed that under a matric suction ranging from 0 to 2000 kPa, the bulk density increased from an initial value of 1.30 g/cm3 to 1.60, 1.72, 1.61, and 1.57 g/cm3 for the soils retrieved from Chanhe, Qingyang, Yan’an, and Lvliang, respectively, resulting in corrected SWRCs considering soil shrinkage that was higher than the uncorrected SWRCs, consistent with previously published work. However, this difference was effectively reduced by retesting the soil samples. A reduction in water volume resulted in the same reduction in the bulk soil volume in the normal shrinkage state, while a shrinkage rate higher than one was found with increasing soil drying. More hydraulically active and connected macropores were detected in the low-density soil. The maximum pore diameter, total pore area ratio (PAR), pore size, and number distribution considerably changed with increasing density. The captured microstructural information is beneficial for the interpretation of the shrinkage behavior and hydraulic properties of soil.