Evaluating the Structural Performance of Stabilized Expansive Soil as Subbase Layer for Sustainable Pavements

The extensive use of aggregates in highway construction has led to the depletion of natural resources, which has given impetus to the use of non-conventional materials. Natural aggregate consumption can be greatly reduced by utilizing improved/lime-stabilized expansive soil as the subbase layer of flexible pavement. This study investigates the same by virtue of laboratory and field scale investigations. Modified proctor test, unconfined compression strength test, and California bearing ratio test were performed on black cotton soil with different proportions of lime (0%, 3%, 6%, 9%, and 12%). The optimum mix of black cotton soil–lime (BCL) with 6% lime was obtained. A thorough structural assessment of flexible pavement test section constructed with optimum BCL subbase enabled substantiation of the BCL mix's superior strength characteristics. The structural evaluation of test sections using a falling weight deflectometer (FWD) demonstrated that a section with a BCL subbase layer displayed 25–30% lower peak deflections than control sections (GSB). From FWD deflection, the back-calculated modulus of the BCL layer is 1.5 times higher than the conventional GSB, which leads to better performance than the GSB, confirming its use to replace the GSB. Additionally, X-ray diffraction (XRD) and scanning electron microscope (SEM) analyses were conducted to validate the improvement in mechanical properties achieved by lime stabilization. Then FEM analysis was carried out using PLAXIS. The service life ratio was improved by 10% and 48% for fatigue and rutting, respectively, using the BCL mix as the subbase layer.