Shear Strength of Unsaturated Soils under Multiple Drying-Wetting Cycles

Under the same stress state, a soil behaves differently when it follows drying and wetting processes because of hysteresis. The purpose of this study was to understand the shear strength characteristics of unsaturated soil under multiple cycles of drying and wetting. A series of unsaturated consolidated drained (CD) triaxial tests were conducted using three different sand-kaolin mixtures. All sand-kaolin mixtures experienced hysteresis during multiple cycles of drying and wetting processes. The CD test results indicated that the specimens on the drying paths have higher shear strengths than those on the wetting paths owing to the hysteresis effects on the soil during drying and wetting processes. The differences between the shear strengths on the drying and wetting paths of the first cycle were found to be more significant than the differences between the shear strengths on the drying and wetting paths of the subsequent cycles. The specimens on the first-cycle wetting path and the subsequent cycles of drying and wetting paths had similar shearing characteristics; generally, they had lower axial strain at failure and exhibited less ductility, more stiffness, and dilative behavior during shearing compared to the specimens on the first-cycle drying path. In addition, the predictions of the drying and wetting shear strengths of different sand-kaolin mixtures as computed from the shear strength equation showed good agreement with the measured data obtained in this study.