Performance of the Tensiometer Method for the Determination of Soil-Water Retention Curves in Various Soils

The soil-water retention curve (SWRC) describes the relationship between the soil matric suction and the water content of an unsaturated soil. It is an essential tool in geotechnical engineering and agriculture and is, for example, used in the analysis of unsaturated soil conditions such as those found in tailings dams and in analyzing the water retention capacity of agricultural land. Conventional methods used to obtain the SWRC are laborious and often rely on empirically derived equations to describe the curve. These test procedures can take weeks to complete and usually rely on indirect methods of measuring suction. Recent advances in the development of affordable high-capacity tensiometers (HCTs), the only devices capable of producing a direct and continuous measurement of high matric suctions, enable the introduction of the tensiometer method for the rapid determination of continuous SWRCs. The method requires an HCT, a digital laboratory balance, and a means of sample volume measurement if volume changes are relevant. The method involves continuously monitoring the mass and matric suctions generated in a naturally desaturating soil sample. The method has thus far seen limited implementation owing to the need for measuring specimen volume change to describe the hydraulic and volumetric behavior fully. The performance of the tensiometer method was investigated by determining SWRCs of five different soil types and then comparing them to the SWRCs determined from the filter paper method. A novel method, based on photogrammetry, was adopted for volume change measurement to produce SWRCs for soils that undergo shrinkage during drying. Excellent agreement between the methods was found for both the nonplastic soils and plastic soils tested.