Damage Assessment of Tunnel Lining by Mobile Laser Scanning: Pittsburgh, Pennsylvania, Implementation Phase of FHWA SHRP 2 R06G Project

Abstract

This paper presents the results of a nondestructive (NDT) laser scanner investigation that was conducted in one night by using the SPACETEC TS3 laser scanner in one tube of each of the Liberty and Armstrong Tunnels in Pittsburgh, Pennsylvania. A portable seismic property analyzer (PSPA), a hand-held NDT ultrasonic seismic device, was used to investigate a 200-ft-long segment of the lining of the Liberty Tunnel, for which results are also presented. The investigation was complemented with a limited inspection with traditional techniques (e.g., hammer sounding, coring) to validate NDT findings. This work was funded by FHWA under the auspices of Round 4 of the Implementation Assistance Program of the SHRP 2 R06G project. Both technologies incorporated in this study were also used and reviewed in the original SHRP 2 R06G project. With the use of the SPACETEC TS3 scanner and the supporting suite of software, the study obtained high-resolution imagery, thermal imagery, and three-dimensional profiles for the full length of the tunnels. The deliverables included complete mapping and inventory of distresses and moisture intrusion behind the lining. In the Armstrong Tunnel, SPACETEC technology was successful at detecting cold anomalies (tile debonding, water intrusion, etc.). However, in the Liberty Tunnel, detection of debonding or delamination was less effective as a result of the insufficient temperature gradient at the time of scanning within this particular tunnel. The PSPA results correlated well with results obtained from traditional techniques. Areas with a lower seismic modulus correlated well with areas showing debonding or delamination. Areas of severe debonding were also clearly identified with the PSPA device.