Modified Campbell (1973) Estimation

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Campbell (1973) presents a method of estimating the permeability curve that can be used in conjunction with a number of methods for representing the soil-water characteristic curve. The Campbell (1973) method as implemented in the SVSOILS uses the Fredlund and Xing (1994) fit of the soil-water characteristic curve as the basis for the permeability function estimation.


Campbell P:

The Campbell P field needs to be checked when the nonlinear least-squares fitting algorithm has been used to determine the optimal fitting parameters based on physical data.


k minimum:

A k minimum value can be entered in this field to represent the minimum allowable hydraulic conductivity. The minimum hydraulic conductivity is reached when the material approaches residual conditions. A minimum value of 1e-14 m/s is typical of the point where vapour flow begins to dominate. When selecting the minimum value of k minimum, it is important to note that there will need to be a significance increase in the number of nodes that may be required when the minimum hydraulic conductivity is less than 1e-10 m/s. It is therefore recommended that a minimum value of 1e-10 m/s be entered for most practical engineering problems. The user is then encouraged to slowly reduce the k minimum value (if necessary) until the model has difficulty in obtaining a solution.


Campbell Predicted:

The Campbell Predicted field indicates whether the estimation algorithm has been successfully executed on the current data.


Campbell Error:

The Campbell Error is the difference between the fitted results and laboratory values in terms of R2.



The Estimate button is provided at the bottom of the dialog in order 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 is important to note that laboratory data will be interpolated on an arithmetic scale.