Influence of repeated drying and wetting cycles on mechanical behaviors of unsaturated soil

A series of tests are performed to measure the variation of deformation and shear strength of unsaturated clays subjected to repeated drying and wetting cycles so as to study the effect of repeated drying and wetting cycles on unsaturated soil by using unsaturated triaxial apparatus. The test results show: firstly, the matric suction of the same soil moisture in SWCC reduces, and shrinkage behaviors of soil enhance during the pre-yield stage of shrinkage and do not change approximately during the post-yield stage of shrinkage; secondly, the compression index increases during the post-yield stage of isotropic compression, and the influence on compression behavior decreases with the increasing suction; and thirdly, a few samples subjected to repeated drying and wetting cycles exhibit a slide plane in triaxal shear tests. Consistently, the stress exhibits an obvious peak value and then decreases sharply with the increasing strain. In addition, repeated drying and wetting cycles not only decrease the triaxal shear coefficient but also have an effect on coefficient with respect to matric suction to a certain extent. It indicates that the change of mechanical properties is irreversible after the unsaturated soil is subjected to repeated drying and wetting cycles.