Ground-penetrating radar for inspection of in-road structures and data interpretation by numerical modeling

In recent decades, road inspections have increasingly relied on the use of nondestructive instrumentation for the evaluation of road conditions. This work aims to test a ground-penetrating radar system to provide insight into nonvisible subsurface engineering with respect to an underpass arch-shaped structure. One important structural parameter that affects the stability of the arch structure and must be monitored is the quantity and thickness of the backfill used to fill the structure until the road is level. Frequencies of 500 and 200 MHz were used to detect the different layers over an arch structure. However, the heterogeneity of the backfill over the arch hampered interpretation of the field data. Finite-difference time-domain modeling was used to understand the response of the radar wave and to assist in interpretation. More realistic models were created based on the accurate geometry provided by a mobile light detection and ranging (LiDAR) device. The methodology is not excessively time-consuming, with all of the procedures taking a total of approximately 7 h. With this system, the layers built and their thicknesses can be defined with a maximum error of 5%. Appropriate nondestructive testing of the subsurface structure is useful in facilitating structural analysis and the prediction of critical failures.