When unsaturated soils are exposed to inundation, they may undergo stress release, which is a significant factor to consider when analyzing the behavior of engineered fills during reservoir impoundment or infiltration. Previous experiments have shown that saturated triaxial samples often experience a drop in deviatoric stress, which is commonly associated with soil structure collapse. However, the exact cause of this stress reduction has not been fully comprehended. To bridge this knowledge gap, this study conducted an experimental program involving triaxial tests on compacted sandy specimens under both saturated and unsaturated conditions. The primary aim was to investigate how sandy soils behave when subjected to saturation or an increase in pore water pressure during triaxial shearing. The researchers also examined how collapse potential and stress state affect the degree of stress reduction. The evaluation of the samples was based on the concept of effective stress. The experimental results demonstrated that stress reduction increases with higher collapse potential, shear stress levels, and confining pressure. Furthermore, stress reduction was observed in both collapsible and non-collapsible samples. This suggests that the stress drop is not solely caused by the collapse phenomenon but is also influenced by plastic deformations resulting from a decrease in mean effective stress.
