ESTIMATION ACCURACY OF SOIL WATER RETENTION FOR THE MODEL USING PARALLEL TRANSLATION INDEX

Abstract

The accuracy of the model for estimating soil-water characteristic curves (SWCC) proposed by Sako et al. is discussed in this study. Specifically, the correlation between the parallel translation index (I_pt) and properties of grain size distribution are investigated. The relationships between fine fraction content, uniformity coefficient, and I_pt was discussed, and linear approximations equation were derived from the relationships. The accuracy of the approximate equations was examined by conducting soil water retention tests on soils of several different grain sizes and comparing laboratory results with calculations. The results showed that the I_pt tended to be larger for the soils with higher fine fraction content and uniformity coefficient. This suggests that more pore water in the soil contributes to suction when the soil has a higher fine fraction. Calculations using the I_pt obtained from the approximations were close to the test results for volcanic sandy soil with fine fraction content of 16%, and 20%. The accuracy of the estimation of soil water retention can be improved by using approximate equations obtained relationship between the properties of grain size distribution and I_pt.