Critical assessment of infiltration measurements for soils with varying fine content using a mini disk infiltrometer

The mini disk infiltrometer (MDI) is used for measuring near-saturated infiltration rates (k_h0) of soils. Because of its compact size, ease of use, and requirement for only a small volume of water, the MDI is handy for laboratory soil specimens (especially in column soil studies). In order to obtain representative infiltration characteristics of laboratory soil specimens, it is necessary to ensure negligible boundary effects on the three-dimensional wetting front propagation beneath the MDI. However, there is no existing study that suggests suitable column dimensions that would be devoid of k_h0 variability because of boundary effects. Moreover, the current approaches in estimating the k_h0 do not adopt measured van Genuchten (vG) soil parameters and rely on empirical vG values. Based on experiments carried out on ten different soils (with varying fine fractions), the current study explores the possible variability in determining a suitable soil specimen diameter to perform an MDI test with no boundary effects. This study is based on 123 infiltrometer experiments conducted on the selected soils and recommends using soil specimen diameters greater than 3.5 times the MDI base diameter for alleviating boundary effects. A power relationship is drawn between k_h0, measured using the MDI, and the fine fractions of soils (percentage finer than 75 microns). The reliability of the current approach in estimating kh₀ using the MDI was evaluated using measured vG parameters.