A field evaluation of an underwater tunnel is conducted using a variety of nondestructive testing (NDT) methods including visual inspection, air-and ground-coupled ground penetrating radar (GPR), ultrasonic tomography (UST), and impact echo (IE). An air-coupled GPR antenna is used along with visual inspection to identify areas of interest in the Chesapeake Channel Tunnel near Norfolk, Virginia. After an example potential damage area is identified using high-speed air-coupled GPR, a robotic scanner was used to automatically scan the area using ground-coupled GPR, UST, and IE. This region is also evaluated using a manually applied UST. This study successfully demonstrates that this particular combination of NDT techniques can efficiently and effectively identify and locate reinforcement, backwall depth, potentially delaminated areas, and even the condition of the bond between the concrete lining and steel reinforcement/backwall.
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