Experimental study of the soil water characteristic curve and unsaturated permeability coefficient based on the evaporation method and combined measuring instrument

Abstract

Objective To determine the reliability and applicability of the soil water characteristic curve and unsaturated permeability coefficient combined measuring instrument designed on the evaporation method, three soil samples were selected: silty clay loam, loam and loamy sand. Methods Under natural evaporation, the evaporation flux, water content, and matric suction at 5 and 10 cm below the surface of the soil column were obtained by using the combined measuring instrument. The measured data were processed based on the linear hypothesis. HYDRUS-1D was used for simulation and inversion, and measured matric suction and flux data were input to determine soil hydraulic parameters. VG-Mualem model was fitted to the processed data by using RETC program. Results The results show that the moisture content accords with the theory of the linear hypothesis, and the linear variation in matric suction is not ideal. However, soil samples other than sandy soil can solve this problem by reducing the evaporation rate and shortening the interval between two measurements. The fitting effect of the test data is good, and the error is small with the simulation result. The unsaturated permeability coefficient measured in the early stage of the test has a large error with the simulated value, which is mainly due to the inability to ensure the accuracy of the hydraulic gradient when the water content is close to saturation. These data can be ignored for improvement. Conclusion It is reliable to use the evaporation method and combined measuring instrument to measure the soil water characteristic curve and unsaturated permeability coefficient.

Keywords

• soil water characteristic curve
• unsaturated permeability coefficient
• evaporation method
• theory of linear hypothesis
• combined measuring instrument