During recent few years, many subgrades and cuttings of Hexu and Hean Expressways were badly damaged due to the swelling action of expansive soils. The purpose of our study was to investigate the swelling mechanism of these expansive soils. A series of tests were carried out, such as X-ray diffraction (XRD), scanning electron microscopy (SEM), cation exchange capacity (CEC), as well as physical and mechanical tests, in this testing program. Results indicated that the swelling behavior of expansive soil was primarily influenced by clay mineral composition, the natural dispersible degree of soil particles, CEC, and microstructure characteristics, etc. Study results suggest that to better understand the swelling mechanism of expansive soil, more attentions should be paid to these factors, particularly mineral composition and soil structure type.
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