Compression–Rebound Behavior and Delayed Deformation Mechanism of Cohesive Soils Under Groundwater Level Fluctuations

Long-term groundwater exploitation causes water-level fluctuations, which are a major driver of land subsidence and infrastructure deformation in sedimentary basins. To investigate the stress-history-dependent compression–rebound behavior of deep cohesive soils, soil samples along the Beijing–Tianjin High-Speed Railway were examined using high-pressure consolidation tests, cyclic loading–unloading tests, SEM, and XRD. Prescribed cyclic effective-stress paths were applied to simulate groundwater-level decline and recovery at different burial depths. The results showed that irreversible deformation was highly concentrated in the early loading stage. Under the groundwater-level decline paths, the first loading cycle alone accounted for approximately 77% and 94.8% of the total cumulative compression in the shallow and deep soils, respectively. During repeated loading–unloading between 0 and P0, the plastic deformation decreased significantly with cycle number, whereas the elastic deformation remained relatively stable. Under the groundwater-level rise paths, the cumulative rebound ratios were only 9.8% for the shallow soils and 17% for the deep soils, indicating that unloading recovered only a small fraction of the preceding compression. In terms of microstructure, the shallow soils had relatively loose and pore-rich fabrics, while the deeper soils exhibited denser particle packing and stronger interparticle contacts. These findings demonstrate pronounced mechanical irreversibility. Together with the measured low permeability, they support a mechanistic interpretation in which slow pore-pressure and effective-stress adjustments may further contribute to delayed deformation. Overall, this study provides a quantitative experimental characterization of the evolution of irreversible compression and incomplete recovery of deep cohesive soils under cyclic effective-stress changes induced by groundwater-level variations.