Use of GPR for Subsurface Pavement Investigations of 23 Airports in South Carolina

Abstract

Ground Penetrating Radar (GPR) has been used as a subsurface investigation tool
in updating the pavement management and maintenance system (PMMS) for the South Carolina
Aeronautics Commission (SCAC). An essential aspect of this system is tracking the deterioration
of the pavement surface condition over time, and determining the load carrying capacity for each
pavement surface. The evaluation reported in this paper addressed this need on 23 airfields by
combining historical records research, visual site inspections, and physical testing. Testing
included FWD measurements, GPR scanning, and coring. The specific objective of the GPR
testing was to determine pavement layer structure information and to identify deeper subsurface
features including voids or foreign objects, such as, abandoned fuel tanks, tree stumps, etc. in
embankments. GPR was used to scan all major pavement elements, including runways, taxiways,
and aprons. The GPR system combined a 1 GHz horn antenna to characterize pavement layer
structure, and a 400 MHz antenna to identify utilities, voids, foreign objects, and areas of high
moisture to a depth of 7 feet. The equipment was set up to travel at speeds of 15-20 mph, and was
equipped with a differential GPS unit to provide a detailed track of the survey paths. The
efficiency of this setup permitted the survey of 2 airports per day on average. The data was
analyzed to identify thickness of the bound and unbound pavement layers. This data was
presented in tabular and graphical form, and was used with the FWD data for back-calculation of
layer moduli. The deeper subsurface features were identified and mapped using geo-referenced
data files. The paper describes the equipment and methodology, the type of data generated, the
methods of data analysis, and representative results.