Research on the Method of Determining Unsaturated Soil Hydraulic Properties by In-Situ or Laboratory Tests

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Knowledge of unsaturated soil hydraulic properties is an essential requirement for prediction of flow and contaminant transport through the vadose zone. It is, however, difficult to obtain unsaturated soil hydraulic properties. Because the method of determining unsaturated soil hydraulic properties is not yet established and there are few data accumulation for Japanese soils. In this research, some new methods to determine unsaturated soil hydraulic properties are investigated. The results obtained in this research are as follows :1. A new method of estimating unsaturated soil hydraulic properties from pF tests in the laboratory or in-situ pumping test data is proposed. In this method a nonlinear least squares algorithm incorporating finite element analysis of non-steady saturated-unsaturated seepage flow is used. The advantages of the proposed method are in the possibility of identifying the optimal unsaturated soil hydraulic properties and diminishing experimental time.2. Soil hydrau … More lic properties are assumed to be represented by van Genuchten's closed-form expressions involving five unknown parameters. These unknown parameters allow great flexibility in the shaped of the hydraulic functions. Therefore when these functions are determined, the cumbersome handling of unsaturated soil hydraulic properties data in models of unsaturated flow can be avoided.3. The proposed method for pumping test data is applicable to the examples of pumping test data which are measured by a hypothetical unconfined aquifer model in the laboratory experiments. Predicted the saturated conductivity and unsaturated soil hydraulic properties are compared with independently determined hydraulic properties for the same soil. Good agreement is found.4. Pressure head data in pF test are measured to judge the equilibrium state of the gravity drainage. Water content versus time measurements are used to estimate three unknown coefficients in the van Genuvhten's expressions. This procedure is applied to Toyoura sand and decomposed granite soil. Less