The soil-water retention curve (SWRC) is an essential tool in geotechnical engineering and
agriculture used in the analysis of unsaturated soil conditions such as those found in tailings
dams and the water retention capacity of agricultural lands. The SWRC describes the
relationship between the soil matric suction and the water content of an unsaturated soil. The
SWRC can be used as a basis to model various unsaturated soil parameters, such as the
hydraulic conductivity and shear-strength functions. It is, therefore, vital that an accurate
characterisation of the SWRC of a soil be made.
Until recently, the methods used to obtain the SWRC have involved obtaining point
measurements along the SWRC and fitting an empirically derived curve through these points.
These procedures can take weeks to complete and usually rely on indirect methods of measuring
soil suction. These factors have limited the widespread use of the SWRC, and therefore, the
adoption of unsaturated soil mechanics into modern geotechnical engineering practice.
The development of high-capacity tensiometers (HCTs), the only devices capable of directly
measuring high soil suctions, has enabled researchers to significantly expand the study into
unsaturated soils and the determination of SWRCs. Toker et al. (2004) introduced a rapid
method for determining continuous SWRCs using an HCT and a digital laboratory balance by
continuously monitoring the mass and suction generated in a drying a soil sample.
This method was investigated by first developing a new low-cost tensiometer capable of
measuring suctions up to 1150 kPa. Simple procedures were developed to reliably saturate and
calibrate the tensiometer without the need for specialised equipment. The SWRCs of five different soil types were determined using the continuous drying method
and then compared to the SWRCs determined from point measurements by the filter paper
method. A novel way of volume change measurement was also incorporated into the method
to produce SWRCs for soils that undergo shrinkage during drying. Excellent agreement
between the methods was found for both the granular soils and fine-grained clayey soils tested.
The method reduced the time taken to determine SWRCs from weeks to mere hours.
Dissertation (MEng (Geotechnical Engineering))--University of Pretoria, 2019.