Swelling yield characteristics of expansive soils under unloaded and loaded conditions

A series of unloaded and loaded swelling rate tests on intact weakly expansive soils with different initial suctions under measuring suction conditions using a consolidation apparatus for unsaturated soils to investigate the yield characteristics of expansive soils under unloaded and loaded conditions during swelling. The study systematically examined the variation patterns of void ratio and suction during the swelling deformation process and explored the swelling yield characteristics of expansive soils. The results show that: The maximum unloaded swelling ratio exhibits a power function relationship with the initial suction, while the maximum loaded swelling ratio follows a logarithmic function relationship with the initial suction, both decreasing as the initial suction decreases. Under loaded swelling conditions, the void ratio decreases as suction decreases, which contrasts with the unloaded condition where the void ratio decreases as suction increases. In the s-p plane, as the net vertical stress increases, the LC yield line exhibits an approximately parallel rightward shift，the SD (Suction Decrease) and SI (Suction Increase) yield lines are nearly parallel and form an obtuse angle with the s-axis. The region enclosed by the LC (Loading-Collapse), SI yield lines, and the s-axis corresponds to the plastic reduction zone of void ratio. The region enclosed by the LC, SD yield lines, s- axis and p- axis represents the plastic increase zone of void ratio, which expands as the initial suction increases. The elastic domain is defined by the LC, SI, SD yield lines and the s-axis, and this elastic domain shrinks as the initial suction increases.