Because tunnels typically service high-volume traffic and operate in aggressive environments, keeping tunnels open during inspection and minimizing tunnel closures and user delays must be carefully balanced with the need to conduct detailed inspections that ensure the safety of drivers. Nondestructive testing (NDT) technologies have the potential to achieve this balance.

This project had five objectives:
     1. To identify NDT technologies for evaluating the condition of various types of tunnel linings and tunnel lining finishes;
     2. To evaluate the applicability, accuracy, precision, repeatability, ease of use, capacity to minimize disruption to vehicular traffic, and implementation and production costs of the identified technologies;
     3. To conduct the required development in hardware or software for those techniques that show potential for technological improvement within the time limitations of this project;
     4. To prove the validity of the selected technologies/techniques for detecting flaws within or verifying conditions of the targeted tunnel components; and
     5. To recommend test procedures and protocols for successfully implementing these techniques.

This research project conducted an investigation of NDT technologies capable of detecting delaminations, voids, and water intrusion—which involved the use of concrete, shotcrete, and steel test specimens. Field validation testing of NDT devices was conducted on tunnels in Colorado; Texas; Virginia; and Helsinki, Finland. This project also investigated the ability of NDT technologies to detect loose tiles and moisture underneath tiles, and it investigated the ability of NDT technologies to measure concrete permeability. The final report documents these activities, and it also recommends test procedures and protocols to successfully implement these techniques.

Project Status: This project is complete.

Product Availability: The final report is available on the following page.