Abstract
Based on tests carried out on a specific device allowing to determine the water retention and transport properties of granular media at low suctions, an alternative approach to Kunze and Kirkham’s method of accounting for the impedance effects due to the high air entry value ceramic disk when using Gardner’s method is proposed. Impedance effects are accounted for by proposing analytical solutions to the equations governing water transfers occurring within the specimen and the ceramic disk. By using some experimental data obtained on a volcanic granular substrate used for urban green roofs, the method is successfully compared to Kunze and Kikham’s graphical method. Its advantages are to be simpler of use and not operator dependent. A detailed examination of the performance of our method compared to those of Gardner and Kunze and Kirkham is carried out based on experimental data, that confirm its validity.
Highlights
TheoryGardner’s method [1] was the first analytical method of calculating the hydraulic conductivity of unsaturated porous media based on the measurement of transient outflow under suction step in the pressure plate apparatus
The method presented in this work originates from an experimental investigation carried out by [7] based on the device represented in Fig. 1, that schematically illustrates the hanging column apparatus used for simultaneous determining the water retention curve (WRC) and the hydraulic conductivity function (HCF)
The experimental data from various materials analyzed showed that the proposed simple analytical method fairly well accounts for the impedance effects of the ceramic disk. This method is believed to be more reliable than Kunze & Kirkham’s graphical method, especially in the case of significant impedance effect, because it is not dependent of the difficulty in choosing the best fitting theoretical curve among the family of curves provided by Kunze & Kirkham
Summary
Gardner’s method [1] was the first analytical method of calculating the hydraulic conductivity of unsaturated porous media based on the measurement of transient outflow under suction step in the pressure plate apparatus. Miller & Elrick [2] were the first to consider the impedance effect, while based on their analytical solution Kunze & Kirkham [3] developed a well-known graphical method This method is nowadays rarely used, since it has been replaced by numerical back analysis methods The method presented in this work originates from an experimental investigation carried out by [7] based on the device represented, that schematically illustrates the hanging column apparatus used for simultaneous determining the WRC and the hydraulic conductivity function (HCF). It consists of a metal cell in which the specimen is placed on a saturated HAEV ceramic disk. The water extracted due to the suction step overflows in the outer tube where the change in water level is monitored by means of a high precision differential pressure gauge ([7])
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