2D/3D Numerical Simulation of Saturated and Unsaturated Soil Characteristics and Comparison with Tension Disc

Importance of determining unsaturated soils hydraulic properties in solute transport and water flow is always regarded by soil science engineers. Among these properties is the hydraulic conductivity that should be determined at different suction. Unsaturated hydraulic conductivity is estimated using the traditional Wooding analysis at steady state condition for tension disc. Estimating of hydraulic parameters using numerical solution of flow equations and the parameter optimization with inverse solution method is one of the conventional methods that its accuracy is dependent on soil type.In this study, saturated and unsaturated hydraulic conductivity was measured in 5 suctions 20, 15, 10, 5 and 0 cm from experiment tension disc on four samples of cylindrical clay soil with diameter of 56 cm and height of 75 cm. Then, the results of tension disc were compared with inverse solution. TheHydrus 2D/3D model was used for inverse solution with Van Genuchten-Mualem method. Optimization process was done based time, cumulative infiltration data, saturated hydraulic conductivity and α parameters obtained from the analysis of the tension disc. Then the optimizedparameters in 2D were used for 3D model simulation. The average standard error of optimized θr, n and L was obtained 0.011, 0.078 and 0.117, respectively. The results showed that the unsaturated hydraulic conductivity obtained from the model is less than the values ​​measured by tension disc. However, the low suctionsindicated betteragreement than higher suctions. Additionally, the maximum and minimum value ofsimulation error ofunsaturated hydraulic conductivity was found in suctions 5 and 20 cm equal to 6.50% and 60.0%, respectively.