Evaluation of Point Pedo-Transfer Functions for the Soil-Water Characteristic Curve

In unsaturated soil mechanics, the soil-water characteristic curve (SWCC) plays a central role in a number of constitutive relationships. The test methods to determine SWCC are adopted or adapted from soil science and agriculture. The PTFs can be grouped into point and parametric PTFs. In this regard, point pedo-transfer functions (PTFs) for SWCC which are heavily used in soil science and agriculture have not found equal prominence in unsaturated soil mechanics. The point PTFs give the water contents at several suctions while the parametric PTFs give the values of the parameters in SWCC equations. The suctions commonly used in point PTFs are 10, 33, 100, and 1,500 kPa. One major problem of PTFs is that each PTF is only expected to perform well for soils of a specific region that it was developed. The objective of this paper is to examine the relevancy of point PTFs in unsaturated soil mechanics by evaluating numerous point PTFs. The evaluation shows that the Gupta and Larson (1979) PTFs at suctions of 10, 33, and 100 kPa and Rawls et al. (1982) PTF at suction of 1,500 kPa performed well. These point PTFs could be used in unsaturated soil mechanics.