Experimental study on long-term rebound characteristics of expansive soil

To investigate the long-term rebound deformation characteristics of expansive soils, a series of confined long-term rebound tests under varying stress levels was conducted on artificially prepared saturated expansive soils with different swelling potentials. The key findings are: (1) During unloading, weak expansive soils demonstrate clear linear rebound characteristics, while strong expansive soils exhibit pronounced nonlinear rebound characteristics. (2) Long-term rebound deformation following unloading consists of two distinct components: primary rebound deformation and secondary consolidation deformation. When the rebound rate of strong expansive soil is less than the ultimate rebound rate, both deformation stages exist. After the rebound rate reaches the ultimate rebound rate, the primary rebound deformation disappears, and the secondary consolidation deformation occupies the entire deformation process. (3) As the free swell ratio of expansive soils increases, so do the compression index, rebound index, and ultimate rebound ratio, while the critical unloading ratio decreases. A strong linear correlation is observed between the ultimate rebound ratio and the free swell ratio. (4) As the free swell ratio increases, the secondary consolidation coefficient grows exponentially, and the onset of the secondary consolidation stage is delayed.