Study On Soil Water Movement Characteristics And Determination Of Hydraulic Parameters Based On Negative Hydrulic Heads

The influence of soil water on soil physical characteristics has exceeded any other elements, which therefore plays a dominant role in soil physics. Meanwhile, study on soil water movement characteristics and determination of hydraulic parameters has become the foundation of quantitative study on soil water. Based on research findings related to the theory of soil water movement characteristics and determination of hydraulic parameters, characteristics of soil water vertical one-dimensional infiltration in four soils under different negative hydraulic heads were studied through theoretical analysis combined with laboratory and field infiltration experiments by tension infiltrometer. Besides, different methods to determine hydraulic parameters of field soil were analyzed and compared. The major results were as follows:(1)Based on Gardner and Gardner-Russo models, coupled with the Darcy law and the Richard equation, infiltration models were developed to describe characteristics of soil water vertical one-dimensional infiltration under a boundary condition of negative hydraulic head. According to the models developed, there exist a linear relationship between infiltration rate and reciprocal of wetting front distance, a proportional relationship between cumulative infiltration and wetting front distance, a parabola relationship between infiltration time and wetting front distance under different negative hydraulic heads.(2)Soil water vertical one-dimensional laboratory infiltration experiments in four soils under different negative hydraulic heads were carried out, and the mutual relationships of cumulative infiltration, wetting front distance, infiltration rate and infiltration time were also discussed. Meanwhile, the applicability of Philip infiltration model and Kostiakov infiltration equation under negative hydraulic head and the theoretical relationships of parametric variables in models developed were verified. The results proved to be justifiable.(3)Soil water vertical one-dimensional field infiltration experiments of Loess Soil under different negative hydraulic heads were carried out, and the mutual relationships of cumulative infiltration, wetting front distance, infiltration rate and infiltration time were also discussed. Meanwhile, the applicability of Philip infiltration model and Kostiakov infiltration equation under negative hydraulic head in field soil was verified, and the relationship between wetting front distance and infiltration time was analyzed by power function as well. The results proved to be justifiable.(4)The soil sorptivity of Loess Soil was calculated through infiltrometer data. The results showed that both Haverkamp method and Smiles method could be used to calculate soil sorptivity of Loess Soil, especially Haverkamp method, whose relative error was minimum.(5)The soil hydraulic conductivity of Loess Soil was calculated through infiltrometer data. The results show that all of the MP, NR and inverse solution could be used to calculate hydraulic conductivity of Loess Soil. However, the saturated hydraulic conductivity estimated by MP and NR were less than measured saturated hydraulic conductivity. Therefore, the inverse solution method was more applicable.