Effect of Cᵣ on the performance of Fredlund and Xing (1994)'s equation in best fitting soil-water characteristic curve data

Abstract

Fredlund and Xing (1994)'s equation is one of most popular equations in best fitting the soil-water characteristic curve (SWCC) data. It is commonly considered that the parameters of the equation such as a, n and m are the fitting parameters and Cr is an input value, which is commonly recommended that Cr to be1500 kPa or 3000 kPa. Based on the analysis in this paper, it is observed that setting Cr to be equal to 1500 kPa or 3000 kPa may downgrade the performance of Fredlund and Xing (1994)'s equation in best fitting the SWCC data of soils with a high air-entry value (AEV). It is recommended the air-entry value (AEV) of the soil is roughly estimated before the best fitting process and set Cr to be 100 times of the estimated AEV for the best regression analysis.