Prediction of unsaturated shear strength of expansive clays

The aim of this study is to predict the unsaturated shear strength of two locally expansive clays available in Saudi Arabia over a wide range of suction. A variety of prediction models categorised as semi-empirical or micromechanical were considered to examine their viability to estimate unsaturated shear strength of these clays over a wide range of suction. Soil water characteristic curves and effective shear strength parameters for both expansive clays were evaluated to serve as input for the prediction of unsaturated shear strength functions (USSFs). To verify the predicted USSF, data for unsaturated shear strength as a function of matric suction were generated from a series of unconfined compression strength (UCS) test specimens with different moisture (suction) levels. Comparison between experimental data and predicted USSF revealed that there is great discrepancy between predicted and experimental data; especially in the high-suction range; this was attributed to the emergence of desiccation cracks during drying. As an alternative approach, function fitting models were used and their viability was discussed.