A Test Method for Soil−Water Characteristics Curve of Unsaturated Loess in the Full Suction Range

The soil−water characteristic curve is an important parameter which reflects the moisture movement characteristic and mechanical behavior in unsaturated soil. A method is proposed based on vapor sorption analyzer combined with transient water release and imbibition method to determine soil−water characteristic curve in the full suction range. First, the relative humidity and the mass of the sample are continuously measured by VSA, series of discrete data points of matrix suction and volume water content are calculated under drying and wetting paths in the high suction range (7.1×10³ ～ 4.8×10⁵ kPa). Secord, the TRIM inversion process is limited through the residual water content of VSA test results. The accuracy of inversion results of TRIM is increased. Finally, the F&X model is used to smoothly connect the test data from TRIM and VSA. The measurement of suction range of this method is wide (1～10⁶ kPa), the measurement time of this method is short (5～8 days), and the measurement accuracy of the method is high (R²=0.999). In this paper, the method is applied to test soil−water characteristic curve of the loess (L₅) and paleosol (S₅) in Dongzhiyuan, Gansu Province. The results show that the predicted results of this method are consistent with the measured results in the full suction range. The method of determining soil-water characteristic curve of unsaturated soil is fast and effective, and important value in engineering application.