Soil-water retention curves of some silty soils and their relations to fabrics

A series of unconfined wetting/drying tests has been conducted on a wide range of silty soils to determine their soil-water retention curves. These soils include a clayey silt compacted at different densities and moisture contents, as well as intact residual soils from various parts of Thailand. The devices used to measure the suction in the tests were a tensiometer, filter paper, and relative humidity sensors. In order to highlight the importance of the fabric of the soil on the water retention curves, a petrological microscope study was also carried out. The bi-modality in retention curve can be observed for the materials with aggregated structure such as silt compacted at a dry-of-optimum moisture content and some natural residual soils at shallow depths. Finally, the Arya and Paris (1981) approach is used to model the retention curves based on the material grain size distribution curve and its dry density. For samples with aggregated fabric and bimodal retention curve, the value of the fitting parameter, a, in the Arya and Paris (1981) model tends to rise to a peak and reduce at an equivalent particle diameter of 0.02 to 0.05 mm. The values of a were found to vary between 1 and 2.