Studies On The Characteristics Of Soil Water Movement And Determination Of Hydraulic Parameters Under Negative Hydraulic Head

Based on the literatures regarding the theory of soil water movement characteristics and hydraulic parameters determination, the methods to determine soil water movement parameters under negative hydraulic heads were discussed by theoretical analysis combined with laboratory infiltration experiments which consisted of horizontal one-dimensional infiltration for different texture soil and vertical one-dimensional infiltration for Huangmian soil. The results were as the follows:1. By horizontal one-dimensional infiltration experiments, the relationships of accumulated infiltration, wetting fronts and infiltration rates with elapsed time for different texture soils under different negative hydraulic heads were analyzed. The suitability of Kostiakov empirical model, Philip model and that developed by Wang(2000) which were used to describe the relationships of soil water movement parameters under horizontal one-dimensional infiltration for negative hydraulic heads conditions were tested and proved to be justifiable.2. Vertical one-dimensional infiltration experiments under different negative hydraulic heads with Huangmian soil were carried out , and the relationships of accumulated infiltration, wetting fronts and infiltration rates with time were also obtained. Meanwhile, the applicability of Philip infiltration equation, Green-Ampt infiltration equation and Kostiakov empirical formula which were used to traditioanlly characterize the vertical one–dimensional infiltration for 0 or positive water heads into negative heads was proved to be justifiable.3.Data obtained with experimental infiltration under negative hydraulic heads was employed to analyze the relationships of Philip model and Kostiakov empirical model. The results showed that they were identical in terms of negative hydraulic heads. The possible relationship between Green-Ampt model parameters and Philip model parameters under negative water heads was verified and found to be in good agreement with the situation under 0 hydraulic head.4. According to infiltration data under negative hydraulic heads, the soptivity of four soils was calculated. The results showed that sorptivity decreased with increasing negative hydraulic head.5. According to Wang (2000), soil infiltration equation could be derived under negative hydraulic heads based on Brooks-corey model and relationships of accumulated infiltration vs wetting fronts, infiltration ratesvs reciprocal wetting fronts and wetting fronts vs time square root were elucidated. The results proved that relationships of the above parameters derived from negative hydraulic heads were coincident with that derived by Wang(2000) under positive hydraulic heads.6.Brook-Corey model parameters of Hongjiao soil, Heilu soil and Lou soil were calculated with the method suggested by Zou (2006) which designed to analyzed infiltration data of two negative hydraulic heads. The result showed that soil moisture characteristic curve calculated based on above derived parameters agreed well with that measured by centrifuge. Van Genuchten model parameters can be theoretically derived under negative hydraulic heads, which provides a new approach to the research of soil water movement and parameter determination.