Evaluation of Lime Stabilized Subgrade

Construction of Section 19 of the Ashland-Alexandria Highway began in 1987. Because native soils have very low CBR values (1 to 3), it was decided to stabilize the soil subgrade with an application of 6% hydrated lime. The top 6 inches of the subgrade was to be stabilized. This process had not been previously used in Kentucky; and consequently, a research study was initiated to monitor this project. Objectives of the study were to monitor and document construction procedures, to determine the engineering characteristics of the treated subgrade through laboratory testing, and to report on the study findings. A substantial amount of field testing was conducted to confirm and supplement laboratory testing. Conclusions drawn from the study were: the addition of hydrated lime to the clay soil produced a desirable end product in which all engineering characteristics of the subgrade were improved, the Special Note for this project did not provide sufficient detail for inspection and acceptance but was revised subsequent to this project, depth of treatment was significantly less than specified, and that lime stabilization can significantly increase the bearing capacity of clayey soil subgrades. Ridges or transverse humps have developed in the pavement surface of Section 19. The ridges were not extensive or of notable magnitude until approximately four years after completion of Section 19. An investigation of the ridges indicated that swell of the underlying Crab Orchard Shale and possibly swell of the untreated clay subgrade produced sufficient pressure to crack the treated subgrade.