Comparison of Measured and PTF Predictions of SWCCs for Loess Soils in China

摘要

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 258rnmeasured 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 cm~3 cm~(-3) as opposed to 0.046 cm~3 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 cm~3 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 cm~3 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.