A Comparative Study of Shear Strength Equations for Unsaturated Granitic Residual Soil

Malaysia is extensively covered by residual soils, which are mostly in an unsaturated zone. Determining the unsaturated shear strength of residual soils using the empirical models is beneficial because of the limitations of experimental methods. Several shear strength models have already been developed, and the accuracy of some of these models has been examined. However, these examinations were developed based only on the particular soils initially studied and may not be applicable to Malaysian residual soils. This study aims to provide a comparative investigation of the accuracy of some of the published shear strength models for unsaturated soils in predicting the shear strength of a Malaysian granitic residual soil. The published shear strength results of the soils were used in this paper to provide comparisons between the predicted and measured shear strength values for a limited suction range. Nine various equations were evaluated. For each equation, a relationship between the predicted and measured shear strength data was generated. The linear regression line with zero intercept was drawn, and the slope of the linear regression line (S_L) and coefficient of determination (R²) were calculated. This study showed that all shear strength models provide relatively acceptable comparisons between measured and predicted shear strengths by a maximum of 10 % difference based on the calculated slopes of the regression lines. However, among them, three equations provided more accurate predictions in comparison with the others.