Abstract:
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.
