On the relationship between plasticity and spectral characteristics of swelling soils: The 3–5 μm wavelength region

Soil swelling is a potential geotechnical hazard that causes considerable problems leading to serious economic consequences in construction sectors, principally light-weight infrastructure development. Simple identification of swelling soils and evaluation of their geotechnical properties is a constant focus of research in geotechnical engineering, including the application of spectroscopic techniques. Potential of laboratory spectroscopy in the 3–5 μm wavelength region was investigated for compositional analyses and classification of swelling soils. Spectra of bulk and fine fraction (passing the ASTM 0.075 mm sieve aperture) soil samples were investigated. The relationships between soil spectra and plasticity were explored using various statistical analyses techniques such as cluster analysis and cross tabulation. Classification of soils based on spectral characteristics showed significant correlations with soil plasticity classes. Strong statistical measures of associations such as high chi-square test statistics, likelihood ratio and contingency coefficients were obtained. Correlations varied from bulk to fine soil fraction. A higher level of agreement with plasticity was achieved for the spectra of fine fraction soils than for the bulk soil samples. The study showed that spectroscopy in the 3–5 μm wavelength region is useful for geotechnical investigation of swelling soils.