Impact of wetting-drying cycles on hydro-mechanical behavior of an unsaturated compacted clay

To further our understanding on the impact of wetting-drying cycles on the hydro-mechanical behavior of unsaturated soils, this paper presents experimental results from suction-controlled isotropic compression tests on an unsaturated compacted clay subjected to different wetting-drying histories. This clay exhibited complicated volumetric response to wetting-drying cycles such as irreversible swelling upon wetting, irreversible shrinkage upon subsequent drying and accumulated swelling after a wetting-drying-wetting cycle. The wetting-induced irreversible swelling contributes to a significant reduction in pre-consolidation stress. It was observed that a wetting-drying cycle leads to a smaller pre-consolidation stress and downward shifting of the post-yield compression curve at a given suction, whereas a wetting-drying-wetting cycle shows an opposite effect. These observations are attributed to both irreversible swelling and irreversible change in the degree of saturation resulting from wetting-drying cycles. It was found that irreversible swelling or an irreversible increase in degree of saturation makes the soil more susceptible to yield, exhibiting a softening effect. Regarding water phase, its response to isotropic compression is mostly related to the recent wetting-drying history rather than the overall wetting-drying history.