Investigation into the shear strength of a weakly expansive soil over a wide suction range

Limited experimental and theoretical research has been conducted on the shear strength of unsaturated soils over a wide suction range. This study aimed to investigate the shear strength characteristics of a weakly expansive soil over a wide suction range (0.05–367 MPa) through a series of triaxial tests. The results of the experiments demonstrate that, under the same net confining stress, the shear strength increases with the suction over the entire suction range. Furthermore, an increase in suction leads to a change in the shape of the stress–strain curve, from strain-hardening to strain-softening. The effect of net confining stress on the stress–strain curve and volumetric strain-axial strain curve varies with suction. An additional analysis indicates that the cohesions and angles of internal friction acquired through net stress differ from those obtained through effective stress. The angles of internal friction at different suctions remain the same on the shear strength-net normal stress ( τ f −( σ − u a )) plane, while the cohesions increase exponentially with increasing suction. Based on these test results, a novel equation for the shear strength of unsaturated soil over a wide suction range is proposed by incorporating suction-dependent cohesion. The results of the study show excellent agreement between the predicted and measured shear strength results over a wide suction range, and its superior accuracy is demonstrated through comparisons with several existing models in the literature.