Measurement Of Water Retention Characteristic Based On Water-air Two-phase Flow In Soil

There are both water and air flowing in soil porosity. The unsaturated flow is acoupled water-air motion. Soil-water characteristic of unsaturated soil is the relationshipbetween suction and permeability and water content, which is explained by the soil-watercharacteristic curve and relative permeability function. This soil-water characteristic ofunsaturated soil, as the basic constitutive relationships to explain the behavior ofunsaturated soil, is a foundation to obtain some important properties of unsaturated soil.Compared to traditional measurements, the method based on the water-air two-phase flowand corresponding experiments can truly reveal the flow process of all phases in soil andthe soil-water characteristic of unsaturated soil.A research on principle and method of measuring soil-water characteristic ofunsaturated soil is done in the paper. Most works are summarized as follows:1) A new method to obtain the soil-water characteristic curve in the unsaturated soilwas proposed based on water-air two-phase flow theory, which includes both numericalinverse calculation and experiment tests.2) An inversion of the soil-water characteristic curve combined numerical solution ofcoupled water-air two-phase flow based on its governing differential equation withmathematical optimization was proposed. A relevant computing program was written, theaccuracy, convergence and numerical stability of which was verified by simulating thedrying and wetting process of soil.3) An experimental system was designed to simulate coupled water-air-flow on thecondition of wetting-drying cycles. In this system, drying-wetting circulation conditionscan be applied automatically according to the state of water flow in soil. And the dischargeof sample can be collected timely to provide the data for numerical inversion calculation.4) The verification and application of the proposed method. The soil-watercharacteristic curve can be obtained by numerical inverse calculation based on dischargedata, bound conditions and initial conditions collected from experiment tests. Thewater-gas flow could be simulated if the measured soil-water characteristic curve wasregarded as the known condition. The accuracy of the proposed method was proved bycomparison and analysis of calculated discharge and experimental discharge.