Prediction of California Bearing Ratio of Soil for Sustainable Road Construction Using Selected Index Properties

The California Bearing Ratio (CBR) test is widely used in pavement design to assess subgrade strength; however, the procedure is laborous, time-consuming, and requires extensive laboratory preparation. In developing countries, where resources and time are often constrained, rapid and reliable prediction of CBR using easily measured soil index properties is essential for sustainable infrastructure development. This study therefore presents an investigation into the prediction of CBR of soil using selected index properties with a view to achieving sustainable road construction. To achieve the aim of the study, twenty (20) lateritic soil samples were collected from selected borrow pits within Ile‑Ife, Osun State, Southwestern Nigeria. The following geotechnical tests were conducted on the soil samples using standard procedure: natural moisture content, particle size distribution, specific gravity, Atterberg limits, compaction, and unsoaked CBR. Statistical analysis using linear and multiple linear regression was employed to establish relationships between CBR and selected index properties such as liquid limit and plasticity index. Results of multilinear regression showed that the best possible combination of the predictors gives a weak relationship between this combination and CBR (R = 0.409, R2 = 0.167, Adjused R2 = -.055, standard error = 4.156. However, a better relationship (linear) was observed between CBR and plasticity index (R2 = 0.512). The developed regression model demonstrates good and promising predictive capability explaining a good proportion of the variation in CBR values. The findings confirm that selected index properties can be reliably used to estimate CBR, thereby reducing dependence on extensive laboratory testing. This approach promotes sustainable road construction practices by minimising cost, time, and material consumption while supporting efficient pavement design. The study, though progressive, contributes to geotechnical engineering knowledge by providing a practical and region‑specific predictive framework applicable to lateritic soils in tropical environments.