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In this study, the effects of vertical strain and hydration time on the mechanical behavior and microstructure of expansive soils are examined, addressing the challenges they pose to engineering structures due to moisture-induced swelling pressure and deformation. Conducting hygroscopic expansion tests on soils with varying initial dry densities, the study explores the relationship between swelling pressure and vertical strain. Additionally, the effect of different hydration times on these properties is assessed. Using mercury intrusion porosimetry, the soil specimens are dissected into top and bottom layers to observe microstructural changes over varying hydration periods. The results indicate a decline in swelling pressure and expansion rate with increased strain; at 1% strain, there is a 54% decrease in vertical swelling pressure and a 41% reduction in lateral pressure. Expansion rate attenuation is more significant, with an 83% decrease in vertical and 92% in lateral rates. The research concludes that the hydration process under limited strain consists of two stages: the initial strain stage, with pronounced top layer expansion, and a subsequent constant-volume stage, where the top layer undergoes compression and the bottom layer expands significantly.

来源平台：INTERNATIONAL JOURNAL OF GEOMECHANICS