Proposed outflow method for the determination of the hydraulic conductivity of unsaturated porous materials

Abstract

Examination of the existing outflow methods reveals that none of the available methods consider membrane impedance without simultaneously involving subjective curve matching. A method is proposed that meets both these requirements and also allows determination of hydraulic conductivity after only small changes of moisture content; the results are therefore easier to interpret. A comparison is made between results obtained from the proposed method and from published outflow methods, as well as from the horizontal infiltration and 'air-pressure' methods. The results obtained exhibit hysteresis for both diffusivity and hydraulic conductivity as functions of moisture content. An hypothesis explaining occurrence of hysteresis in hydraulic conductivity at low moisture contents is presented. It is concluded that the proposed outflow method is experimentally suited to the dry end of the moisture content range, because of the restriction imposed at high moisture contents by the membrane impedance being large relative to the sample impedance. A simple criterion to determine the range of validity of the method is proposed.