1319 
A MULTIVARIATE REGRESSION ANALYSIS FOR DERIVING ENGINEERING 
PARAMETERS OF EXPANSIVE SOILS FROM SPECTRAL REFLECTANCE 
Fekerte Arega Yitagesu, Freek van der Meer, Harald van der Werff, Wolter Zigterman 
International Institute for Geo-information Sciences and Earth Observation, ESA Department, P.O. Box 6, 99 
Hengelosestraat, 7500AA Enschede, yitagesu@itc.nl; vdmeer@itc.nl; 
-vdwerff@itc.nl The Netherlands 
Commission VII, WG VII/7 
KEY WORDS: Expansive soils, PLSR, spectroscopy, engineering parameters, absorption feature parameters. 
ABSTRACT: 
Soil expansiveness is a major problem that need due attention in geotechnical investigations. It can detrimentally influence 
performance and life time of lightweight engineering infrastructures. For this study, soil samples were collected from eastern part of 
Addis Ababa city. Specific expansive soil engineering parameters; Consistency limits (liquid limits (LL), plastic limits (PL) and 
plasticity indices (PI)), free swell and cation exchange capacity were measured in a soil mechanics laboratory. Reflectance spectra of 
each soil 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 absorption 
feature parameters calculated from the reflectance spectra of expansive soils at specific wavelengths (~1400 nm, — 1900 nm and 
~2200 nm). Correlation coefficients obtained showed that a large portion of the variation in the engineering parameters (R=0.85, 
0.86, 0.68, 0.83 and 0.64 for CEC, LL, PL, PI and FS respectively) could be accounted for by the spectral parameters. Results of the 
prediction models are high, indicating potential of spectroscopy in deriving engineering parameters of expansive soils from their 
respective reflectance spectra, and hence its potential applicability in geotechnical investigations of such soils. 
1. INTRODUCTION 
Expansive soils are major geotechnical hazards that can pose 
severe limitations on performance and life time of light weight 
engineering infrastructures. Major problems are: volume 
changes due to swelling and shrinking, which can lead to 
differential settlement and creep; decrease in bearing capacities 
and shearing strength when saturated; high erosion 
susceptibility when exposed in cuts or open excavations and 
difficult workability conditions (Figure 1 shows problem on 
road infrastructure). The problem is world wide (Al-Rawas, 
1999; Chen, 1988; Goetz et al., 2001; Gourley et al., 1993; 
Kariuki et al., 2004; Nelson and Miller, 1992; Ramana, 1993; 
Shi et al., 2002) though particularly prone are places where 
there are significant climatic variations between dry and wet 
seasons. 
Figure 1. Failure of road pavement due to presence of exposed expansive soils beneath the side slope of road embankment (left), 
road side drain or ditch clogging due to slumping of expansive soil from bare back slope (right).