Investigation of Swelling Clay Soils in Subgrades of SH 6 and SH 21 (2965-1F)

In the Bryan District, SH 6 and SH 21 are experiencing severe pavement distortion in several locations causing an exceptionally rough ride. Routine site investigation prior to construction did not reveal underlying soil conditions that could produce the kinds of pavement distresses that appeared relatively soon after pavement construction was completed. These 2 areas were investigated using innovative, state-of-theart field and laboratory testing techniques to determine the origin(s) of the pavement distresses manifested at the surface and to determine what could be done to alleviate the existing pavement surface problems or what site investigation techniques should be employed in the future to circumvent the recurrence of these types of problems.Specific objectives of the research study were to conduct detailed site investigations using state-of-the-art techniques, analyze data to isolate cause(s) of the pavement distress, suggest alternatives to stabilize the swelling soils, recommend site investigation techniques to identify similar problem soil profiles in future construction sites, and develop treatments to stabilize such soils and, thus, minimize pavement distress.Findings indicated the swells were not caused by lime stabilization of sulfate bearing soils but were the result of surface water flowing through deep cracks or permeable soil layers to highly plastic expansive clays. Recommended remedial actions to reduce subsequent swelling and site investigation procedures to detect potential problems during the construction process are given.