Laboratory versus field values of unsaturated soil diffusivity

摘要

Unsaturated moisture diffusivity measurements in the laboratory are typically substantially lower than those back-calculated from moisture-suction profiles measured in the field. These differences are probably higher due to cracks and root-holes in the soil. The cracks may develop as a result of desiccation of the soil, which is strongly influenced by surface vegetation. The occurrence of the cracks varies with depth - more at the surface and less at the deeper elevations. However, this process mightreverse to some extent in the case of a rainfall or surface watering - closing the cracks at the shallower depths and thus changing the moisture diffusivity. This paper contrasts laboratory measurements of unsaturated soil diffusivity with typical fieldvalues measured at other sites for similar soil conditions. The laboratory diffusivity coefficients are determined on a number of Shelby tube samples obtained from field borings extending up to 6 meters. Unsaturated soil moisture diffusivity are measured in the laboratory by following the testing protocol described in the Paper "Unsaturated Soil Diffusivity Measurements" submitted to this Symposium by the same authors. The field values of diffusivity considered in the paper are based on values back-calculated from moisture-suction profiles reported from various sources. Tentative recommendations are provided for relating laboratory measurements of diffusivity to values that can be anticipated in the field.