A study on the correlation relationships between smectite contents and spectral absorption indices of swelling soils

55 surface and sub-surface samples of expansive soils were collected. Clay mineral composition and smectite contents were measured using XRD and dye absorption methods. The effective smectite contents were calculated. Meanwhile, the visible-short wave infrared spectra of the swelling soils was collected, the spectral absorption indices, such as wavelength position, depth, width, asymmetry, area, were calculated automatically. Then, the correlation relationships between the spectral indices and the smectite contents and the colloid contents and clay contents of the swelling soils were statistically analyzed. The results show that the very high, high, medium, weak potential soils can be identified according to the relative strengths of the 2200 nm, 1900 nm, 1400 nm absorptions in the spectral features of the swelling soils. The laboratory spectral measurement and analysis techniques to the dried and homogenous swelling soils can be productively used for quickly, economically, and conveniently identifying swelling soils, estimating the contents of smectite, colloid, and clay in fields.