Effect of range of soil–water characteristic curve measurements on estimation of permeability function

• Four different ranges of SWCC measurement were considered, namely DR1, DR2, DR3 and DR4.
• Twelve estimation permeability models were used.
• The range of SWCC measurements greatly affects the estimated permeability functions.
• The effect of the range of SWCC measurements is more significant than the selected best-fit SWCC equation used.

The most commonly used indirect method to determine unsaturated permeability of soil is to estimate the unsaturated permeability function from soil–water characteristic curve and saturated permeability. The suction range that soil–water characteristic curve (SWCC) can be measured in the laboratory depends on the type of equipment used for measurement. As the estimation models use the available measured SWCC data to obtain the unsaturated permeability function, the estimated permeability function can be affected by the number of measured data of SWCC and the suction range over which the SWCC data are measured. Therefore, there is a need to investigate the effect of the range of SWCC measurements on the estimation of unsaturated permeability function. In this study, the effect of the range of SWCC measurements is investigated through different estimation models that are based on four different best-fit soil–water characteristic curve equations and three different relative permeability equations. It was found that the range of SWCC measurements greatly affect the estimated permeability functions. It was also found that the effect of the range of SWCC measurements is more significant than the selected best-fit SWCC equation used.