NMR-Based Measurement of AWRC and Prediction of Shear Strength of Unsaturated Soils

Abstract

In recent years, accurate determination of the effective stress factor has been found to be instrumental for classifying the types of pore water and defining the form of their contribution to the unsaturated soil strength. In this study, a series of laboratory experiments based on volumetric flask, indoor evaporation and low-field nuclear magnetic resonance (NMR) methods were conducted on Wuhan clay to determine the relationship between adsorbed water content and matrix suction, and hence the adsorbed water retention curve (AWRC). The capillary water retention curve (CWRC) is the curve derived by subtracting the AWRC from the soil water characteristic curve (SWCC). This CWRC is then utilized to obtain correlation between the degree of saturation of capillary pores (Scap) and the matrix suction. The effective stress factor was replaced with Scap for determining the shear strength of Wuhan clay with three different dry densities. It was observed that the predicted values of shear strength obtained by NMR-based methods are more accurate than two other methods available in the literature. Furthermore, the accuracy of the method is not impacted by changes in dry density or confining pressure.