Infrasense recently carried out a subsurface pavement structure evaluation on 8 miles of Interstate 85 between Gaffney, South Carolina, and Grover, North Carolina. To determine the thicknesses of the pavement structure layers, ground penetrating radar (GPR) was used in the field testing program which included continuous data collection along the right shoulder in each direction of Interstate 85, from milepost 98 to milepost 106. The data was collected at driving speed, so traffic flow was not disrupted. The deliverables for this project included continuous layer thickness information provided in tabular and graphical formats. The results will be used as part of a rehabilitation design effort, and to ensure the shoulders can support traffic that is redirected during construction.
The GPR equipment used for this survey included a 1GHz horn antenna and SIR-30 data acquisition system, both manufactured by GSSI of Nashua, NH. The 1GHz antenna is particularly well suited for pavement evaluations as it provides an optimum balance of resolution and depth of penetration. Using this equipment, and in-house analysis software, the GPR layer thickness results are typically within 10% of core thickness values.