The relationship between the shear strength and water retention curve of unsaturated sand at different hydraulic phases

This technical paper focuses on evaluating the shear strength of unsaturated sand at drying, wetting and alternate drying–wetting cycles, as well as the correlation between the strength and the water retention curve (WRC) at different hydraulic phases. Results of stress–strain curves and WRCs were obtained from conducting numerous tests using suction-controlled triaxial test. Although the maximum shear strength was obtained from the specimens under drying conditions, the difference between the drying and wetting shear strength was relatively small for the tested soil. Based on analysis of the test results, a multi-surfaces envelope model was proposed to fit the experimental shear strength data under drying conditions and to predict the shear strength under wetting conditions (or any subsequent drying–wetting cycle) based on the drying fitting parameters. The fitting and prediction performance of the proposed equations were checked using experimental data from previous studies, and very good agreement was reported. Moreover, the WRC was found to be capable of not only estimating unsaturated soil property functions but also anticipating the soil shear strength behaviour under different hydraulic phases.