Comparison of Measured and PTF Predictions of SWCCs for Loess Soils in China |
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| Authors: | Mingbin Huang D G Fredlund M D Fredlund |
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| Institution: | (1) Institute of Soil and Water Conservation, CAS & MWR, Northwest A&F University, Yangling, 712100 Shannxi, China;(2) Golder Associates Ltd, 1721, 8th Street East, Saskatoon, SK, S7H 0T4, Canada;(3) SoilVision Systems Ltd, 202, 640 Broadway Avenue, Saskatoon, SK, S7N 1A9, Canada |
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| Abstract: | There are significant advantages in using indirect pedo-transfer functions, (PTFs) for the estimation of unsaturated soil
properties. The pedo-transfer functions can be used for the estimation of the soil–water characteristic curve (SWCC) which
in turn is used for the estimation of other unsaturated soil properties. The accuracy of the indirect pedo-transfer function
method for the estimation of the SWCC depends on the PTF and the equation used to best-fit the particle-size distribution
(PSD) data. The objectives of this study are to: (1) evaluate the performance of the Fredlund et al. (Can Geotech J 37:817–827,
2000) equation for best-fitting the particle-size distribution, (PSD) data, and, (2) compare the predictions made by two of the
commonly used PTFs; namely, Arya and Paris (Soil Sci Soc Am J 45:1023–1030, 1981) and Fredlund et al. (Can Geotech J 39:1103–1117, 2002), for estimating the SWCC from the PSD. The authors used 258 measured PSDs and SWCC datasets from the Loess Plateau, China,
for this study. The dataset consisted of 187 silt–loam soils, 41 loam soils, 11 silt–clay–loam soils, 10 sand–loam soils,
6 silt–clay soils, and 3 loam–sand soils. The SWCC and PSD datasets were measured using a Pressure Plate apparatus and the
pipette method, respectively. The comparison between the estimated and measured particle-size distribution curves showed that
the Fredlund et al. (Can Geotech J 37:817–827, 2000) equation closely prepresented the PSD for all soils in the Loess Plateau, with a lower root mean square error (RMSE) of
0.869%. The comparison between the estimated and measured water contents at the same suction showed that the Fredlund et al.
(Can Geotech J 39:1103–1117, 2002) PTF performed somewhat better than the Arya and Paris (Soil Sci Soc Am J 45:1023–1030, 1981) function. The Fredlund et al. method had RMSE value of 0.039 cm3 cm−3 as opposed to 0.046 cm3 cm−3 for the Arya and Paris (Soil Sci Soc Am J 45:1023–1030, 1981) method. The Fredlund et al. (Can Geotech J 39:1103–1117, 2002) PTF produced the closest predictions for sand–loam, loam–sand, and loam soils, with a lower RMSE for gravimetric water content
ranging from 0.006 to 0.036 cm3 cm−3. There were consistent over-estimations observed for silt–loam, silt–clay–loam, and slit–clay soils with RMSE values for
gravimetric water content ranging from 0.037 to 0.043 cm3 cm−3. The measured and estimated air-entry values were closest when using the Fredlund et al. (Can Geotech J 39:1103–1117, 2002) PTF. The measured and estimated maximum slopes on the SWCC were closest when using the Arya and Paris (Soil Sci Soc Am J
45:1023–1030, 1981) PTF. |
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