Measurement of pressure-saturation hysteresis curves for three liquids in Vinton fine sand

Abstract

Measurement of water is important in soil since this is the medium in which soil activity takes place. Pressure-saturation curves show the extent of liquid retention in the soil porous medium at different tensions during drainage and sorption (hysteresis). Measurement of soil moisture in the laboratory is time-consuming, labor-intensive and expensive. In this study, three methods for measuring pressure-saturation curves were employed, Hanging Water Column (HWC), Differential Pressure Transducer-Imbibition, and Differential Pressure Transducer-Natural. The standard HWC is compared to the other two methods which employ external manometer pressure and differential pressure transducers. Hysteresis pressure-saturation curves were determined for three liquids (water, 50% ethanol and 100% ethanol), in a homogeneous Vinton fine sand. Data was fit to the van Genuchten and Brooks Corey models and liquid capillary numbers are compared. Prediction of desorption pressure-saturation curves from water curves using relative surface tension ratios is discussed and prediction of sorption curves using relative A parameters for the drying and wetting curves. Scanning curves were scaled from the main drying and wetting curves. The capillary number-pore water velocity combination function could be another useful relationship for pressure-saturation curves. Overall, the differential pressure transducer methods were found superior to the HWC because time consumption was reduced by more than 50% yet the results obtained were of comparable accuracy. Pressure-saturation curves for other liquids may be predicted by scaling pressure and van Genuchten alpha parameter with relative surface tension ratios. Hence, hysteresis curves can be obtained faster and the main disadvantages of time-consumption, labor and cost are eliminated. In addition, handling of hazardous liquids in the laboratory is minimized which is important because understanding retention of hazardous chemicals in soil is a prerequisite to achieving remediation of residual contamination. Functional relationship between the residual nonwetting phase and the capillary number or viscosity to surface tension ratio is briefly discussed.