Nondestructive Testing Methods for Underwater Tunnel Linings: Practical Application at Chesapeake Channel Tunnel

Abstract

A field evaluation of an underwater tunnel was 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 was used along with visual inspection to identify areas of interest in the Chesapeake Channel Tunnel near Norfolk, Virginia. After potential regions were identified, a robotic scanner with pneumatically driven suction feet was used to automatically scan the area using ground-coupled GPR, UST, and IE. Regions were also evaluated using manually applied UST. These methods combined with powerful software presented the element under inspection as a 3D volume for thorough inspection. This study shows that this particular combination of NDT techniques can efficiently and effectively identify and locate reinforcement, backwall depth, and potentially delaminated areas. By analyzing the phase shift of ultrasonic waves, it is also shown that UST techniques can be used to potentially determine the condition of the backwall and reinforcement bonding.