| As traffic volumes grow and pavements age, city streets in urban areas are vulnerable to the potentially dangerous problems such as subsurface voids. These subsurface voids can significantly reduce the bearing strength of pavements and eventually result in the collapse of city streets. Several nondestructive testing (NDT) methods have been studied to detect subsurface voids during the past two decades. However, these studies mainly focused on detecting small voids close to the surface of the highway pavements. As far as urban area is concerned, few studies have been conducted to evaluate the capacities of NDT methods to locate subsurface voids. Moreover, congested and complex subsurface circumstance makes it more challenging to evaluate subsurface conditions.; This research project was an attempt to comprehensively study the principle of Ground Penetrating Radar (GPR) applied to locate subsurface voids under pavements. An equivalent 50 linear miles GPR survey was conducted by using a 400 MHz antenna in the urban area in downtown Louisville, Kentucky. A database of GPR signals within urban environment was created. This database comprised of a catalog of GPR signals representing reinforcements, concrete pipes, trolley tracks, and subsurface small and large voids. The validity of GPR patterns was verified by excavating the suspected areas. The results proved that GPR method is an effective method to detect subsurface voids. The acquisition, post processing, and interpretation of the data were conducted. Finally, the limitations of GPR and recommendations are discussed. |
