Fredlund, Xing and Huang (1994) Estimation 
Fredlund, Xing and Huang (1994) presented a modification of the Mualem (1976) integration method of estimating the hydraulic conductivity of a material as a function of soil suction. The integration procedure is complex and a closedform solution is not available.
k minimum: The k minimum value entered in this field represents the minimum hydraulic conductivity allowed. The minimum hydraulic conductivity should generally correspond to the permeability near residual suction conditions. A suggested minimum value of 1e14 m/s is suggested. It is important to note that there may be a significant increase in the number of nodes required when the minimum hydraulic conductivity is less than 1e10 m/s. It is suggested that a minimum permeability value of 1e10 m/s be used for most practical problems. It is also possible for the user to slowly reduce the minimum permeability value until the model has difficulty achieving convergence.
Apply k minimum: The equation originally presented by Fredlund, Xing and Huang (1994) did not have a limitation on the minimum hydraulic conductivity allowable. Applying a reasonable minimum to the unsaturated permeability function data can dramatically improve numerical computations.
Fredlund Predicted: The Fredlund Predicted field indicates whether the estimation algorithm has been successfully executed on the current data.
Fredlund Error: The Fredlund Error is the difference between the fitted results and the laboratory values in terms of R2.
The Estimate button is provided at the bottom of the dialog to allow the user to estimate the hydraulic conductivity.
The Graph button allows the user to display a graph of suction versus hydraulic conductivity. The interpolated curve will also be displayed. It should be noted that the permeability data will be interpolated on an arithmetic scale basis.
