Assessing expansive soil engineering parameters using spectroscopy

Presence of expansive soils in construction sites has serious implications on planning, design, construction, maintenance, and overall performance especially of lightweight engineering infrastructures. Such soils are particularly susceptible to considerable volume changes in response to moisture content fluctuations following seasonal climatic variations. This property can cause severe damages to infrastructures unless proper measures are taken in their design. Identification of expansive soils and characterization of their anticipated behavior is thus important for site selection, design, and construction. In this study, specific expansive soil engineering parameters; consistency limits (liquid limits (LL), plastic limits (PL) and plasticity indices (PI)), free swell (FS), cation exchange capacity (CEC) and California bearing strength (CBR) were measured in a soil mechanics laboratory. Reflectance spectra of each soils sample were acquired in a remote sensing laboratory using ASD fieldspec full range spectrometer. A multivariate calibration method, partial least squares regression (PLSR) analysis, was used to relate engineering parameters and spectral parameters extracted from the reflectance spectra of expansive soils. Correlation coefficients obtained showed that a large portion of the variation in the engineering parameters (e.g. r=0.85, 0.86 for CEC and LL respectively) could be accounted for by the spectral parameters. The results indicate potential of spectroscopy in providing estimates of engineering parameters of expansive soils (e.g. subgrade characteristics), which can be useful in site selection, route planning and search for construction materials (borrow, subbase etc).