Hydraulic Parameters Measurements And Estimations For Loess Soils

Accurate measurement and estimation of hydraulic parameters are the basic to simulate soil water flow. Soil water characteristic curve, soil hydraulic conductivity and soil water diffusivity are the important parts of hydraulic parameters. Direct measurement method is expensive and time costing, the accuracy of indirect method was uncertain with model types, and soil physic and chemical properties, so it is essential to choose different estimating methods with different soils. We discovered an instrument to measure soil water diffusivity by improving horizontal column infiltration, and have measured four soils'(Yangling heavy loam, Changwu medium loam, Ansai light loam and Shenmu Sandy soil) water diffusivity using it. The results were compared with horizontal column infiltration method. The hydraulic properties of Loess soil were estimated from soil basic physical properties. The fitting effectiveness of ten soil particle-size distribution models were compared for Loess soil and the accuracies were evaluated using physical empirical model-AP model and fractal geometry model-TW model to estimate soil water characteristic curve. The hydraulic conductivities were estimated using Brooks-Corey-Burdine and van Genuchten-Mualem models and soil basic properties.The results indicated that:(1)There were not significant difference for soil hydraulic diffusivities measured by disc diffusion and horizontal column infiltration methods, which proved that the disc diffusion method is reliable. Compared with horizontal column infiltration method, the advantages of disc diffusive instrument are to measure more than one sample at the same time, to reduce experimental error via replications, and to improve efficiency.(2)Compared with the compatibility of ten general soil particle-size distribution models on the Loess soil, the fitting effectiveness of Fredlund model with three parameters was the best.(3)Using soil basic physical properties to estimate loess soil water content characteristic curves, we found that the good results were obtained by using both the AP and TW methods. Comparatively, the AP method was better than TW method, and the AP method was less influenced by soil texture than TW method.(4)BC-B and the VG-M methods both can estimated hydraulic conductivity for loess soils with soil basic parameters. Comparatively, the BC-B method was better for coarse textured soil, and VG-M method was better for fine textured soils.