Case Study on Tunnel Lining Assessment Using Stress Wave-Based Nondestructive Testing Methods

A condition survey of a plenum and roadway wall in Chesapeake Channel Tunnel in Virginia was carried out using two seismic nondestructive testing methods: ultrasonic surface waves (USW) and impact echo (IE). These two test methods were performed simultaneously with a portable seismic pavement analyzer (PSPA). The applicability and accuracy of each method and the combined IE-USW method in assessing tunnel liners is investigated. At intact areas, the IE method can provide the thickness of the concrete lining and roadway wall, and the USW method can provide the average modulus as an indication of the quality of concrete. On the other hand, at defective areas, the IE method exhibited frequency peaks different than the expected thickness frequency, and the USW method shows lower moduli as compared with the modulus of concrete in intact areas. About 2600 ft (800 m) of the plenum and 200 ft (60 m) of the roadway wall were involved in this study. The selection of testing areas was based on the visual inspection and the measured surface dielectric constant by other nondestructive testing methods. Results from this study demonstrate that a combination of USW and IE methods yields similar defect maps. The location, depth and severity of problematic areas can be interpreted by combing the USW and IE results. These complementary combined results build confidence in detection of defected areas, and have the additional advantage that no additional time is needed to collect the combined field data compared to collection of one or the other of the data types alone.