Swelling Bulk Density and its Application in Arya and Paris Model for Soil Moisture Curve Prediction

One of the Arya and Paris model (AP) drawbacks is setting saturated water content (θs) equal to total porosity (f=1-ρb/ρp), in which ρb and ρp are soil bulk and particle densities, respectively. For swelled soils with θs greater than f, using AP model leads to under prediction of water content at the measured suction values. The aim of this study was to introduce swelling bulk density (ρbs,: defined as the ratio of dry soil weight to its swelled volume) and its application in AP model to improve model efficiency for swelling soils. For this, we used 22 soil samples to check the accuracy of the model after improvement. Application of the ρbs improved the accuracy of the model compared to the conventional ρb. Employing ρbs instead of ρb increased the R2 between measured and predicted water contents from 0.740 to 0.790 with a constant a 0.648 and 0.699 for variable a. Moreover, the intercept and slope of the regression line approached to 0 and 1, respectively.