Identifying Acceptable California Bearing Ratio (CBR) Value for Kansas Subgrades Using Pavement Rutting Data

This study identified a statistical correlation between rutting evolution and subgrade strength, based on which a minimum acceptable subgrade strength expressed in terms of California Bearing Ratio (CBR) value was proposed. Weak subgrade condition can cause excessive rutting, which is a major type of distress in flexible pavements. Hence, a minimum subgrade strength is required to prevent unacceptable pavement rutting. The data used in this study were selected from pavements located in seven counties in Kansas. Dynamic Cone Penetrometer (DCP) tests were performed in the subgrade of selected pavement locations. Corresponding CBR values were obtained from DCP using an empirical correlation. In the statistical model, the correlated CBR was used as independent variable and average change in rutting was used as a dependent variable. Statistically significant correlation with 0.001 significance level was observed between the CBR and rut development in the pavement. Finally, a criterion for selecting the minimum acceptable CBR of subgrade was proposed.