The work in this report is focused on performing full-scale testing in the field on instrumented unpaved roadway sections to collect data for the validation of guidelines developed from the laboratory and modeling study. Four 16 feet wide by 50 feet long stabilized test sections were built on poor subgrade soils encountered in the Coastal Plain region of North Carolina. One test section encompassed undercutting and replacement with select material (Class II), the second and third test sections included reinforcement using a geogrid and geotextile, respectively, in conjunction with undercutting and replacement with ABC (Class IV), and a fourth test section included cement treatment of the soft subgrade soil. Full-scale testing was conducted on the test pad by applying 1000 consecutive truck passes using a fully loaded tandem-axle dump truck over a period of four days. During this time visual observations were noted and measurements were collected regarding rut depth, vertical stress increase at the base/subgrade interface, and subgrade moisture content with truck passes.
Once trafficking was completed, the test pad was re-graded and proof roll testing was performed to look for signs of pumping and rutting. Based on the field results, the proposed undercut criteria are evaluated in regards to the ability to discern the need for undercutting as well as predict the performance of the stabilized test sections. Finally, a performance cost analysis is conducted to illustrate the relative cost of each stabilization measure in relation to the measured performance (rutting) such that an informed decision on cost-effective subgrade stabilization can be made.
