Resistivity Method To Calculate The Soil Water Characteristic Curve

Soil Water Retention Curve(SWRC) plays an important role in soil science. A series of important soil physical parameters, such as unsaturated hydraulic conductivity, Soil moisture regime and permanent wilting point can be obtained easily from it. Moreover, SWRC can predict the migration behavior of chemicals and water in soil. However, due to the complicated effects from the environment and soil factors, the direct measure of SWRC is toilsome, expensive and time consuming. The indirect estimation of SWRC needs a great deal of data, and the accuracy is limited. Because of the horizontal and vertical spatial variation of soil, the prediction of SWRC on regional scale is considerable difficult. Thus the precise prediction of unsaturated zone SWRC on the regional scale spatially and temporally is significant and important for monitoring and managing the migration of chemicals and water. Meanwhile, it would be benefit for the management of field moisture.In this paper the soil resistivity and corresponding moisture content of the soil (sampled from Jimo, Qingdao) was surveyed by using self-made equipments, and the SWRC is obtained from the "Ku-pF apparatus". Via the ratio between bulk resistivity of saturated soil and measured data, we excluded the influence from the resistivity of pore-water, pore size distribution, soil particle composition and other proprieties of soil, simplified conventional method which concerns resistivity of pore-water, facilitated the investigation and application of resistivity method.Firstly,1stOpt software was used to fit the measured data to obtain the parameters of resistivity-moisture model and SWRC Gardner model. Secondly, the relationship between resistivity and matric suction was constructed through moisture content, and the resistivity-matric suction model was proposed which would be an alternative method to predict the soil matric suction. Then, combined resistivity-matric suction model and resistivity-moisture model, the application of resistivity in assessing SWRC was discussed. It is completely coincidence between the SWRC from tested result and resistivity method. Thus the resistivity method makes the prediction of SWRC possible on the regional scale spatially and temporally, and the application of resistivity method in soil science is expanded. The research results are listed as follows:(1)The SWRC of loam and clay in this region were obtained, which can provide a series of important soil physical parameters, such as unsaturated hydraulic conductivity, soil moisture regime and permanent wilting point. The data of moisture content and matric suction is obtained from the "Ku-pF apparatus", which was fitted by lstOpt with Gardner model. The SWRC of loam and clay in this region provide the basis for predicting the migration behavior of chemicals in soil and managing the moisture of field.(2) The parameter n in resistivity-moisture content model and saturated soil resistivity ρs of loam were obtained, which provide references for the resistivity application. The resistivity-moisture model is not suited in clay, because the electric conductivity of particle surface in clay is not ignorable in the quantify research. The four-electrodes method is better than the two-electrodes method in the measurement in soil resistivity. An equipment was designed using four-electordes method to determine soil resistivity in laboratory, which makes the measure of soil resistivity more convenient.(3) The soil resistivity-matric suction model was proposed, which might be an alternative method in predicting the soil matric suction in soil science, hydrogeology and engineering geology. In he regional scale,using the resistivity method through the one-time laid electrodes in space, the soil matric suction can be predicted in space, which is more advantages than other method, especially in determining the stability of Slope in engineering geological exploration slopes.(4) A new method was developed for the SWRC measurement. Using resistivity, an accurate SWRC can be obtained spatially and temporal in undisturbed way. Meanwhile, the difficulties resulted from horizontal and vertical spatial variations of soil were solved.