Approach to Rapidly Determining the Water Retention Curves for Fine-Grained Soils in Capillary Regime Based on the NMR Technique

A new procedure is developed for rapidly determining the water retention curves of unsaturated fine-grained soils based on the nuclear magnetic resonance (NMR) technique. From a well-defined pore-size distribution function, a distribution function of NMR transverse relaxation time ($T_2$ ) is derived for fully-saturated soils, by virtue of the Young-Laplace equation and the linear relationship between pore radius and $T_2$ . By fitting the measured $T_2$ distribution curve with the proposed $T_2$ distribution function, the key parameters characterizing the soil-water retention characteristics can be determined. To validate the proposed method, a series of the NMR measurements was performed for two types of fully-saturated fine-grained soils. The proposed procedure is then used to obtain the soil-water retention curves of the tested soils from the NMR measurements; the obtained soil-water retention curves are compared with those determined independently by the pressure-plate method. It is shown that the proposed procedure can be effectively used to determine the soil-water retention curves of fine-grained soils in a capillary regime. Compared to conventional methods, which are generally time-consuming, the proposed procedure can save a significant amount of time in determining the soil-water retention curves.