City of Bellingham Tunnel Inspection
2G Robotics enabled the City of Bellingham to accurately model the current state of their main water-supply tunnel.
The City of Bellingham was seeking a way to inspect their main water-supply tunnel without adding stress by draining the tunnel as they had historically done. The goal of the inspection was to assess the current condition and shape of the tunnel. Without an inspection, the city would have been placed in a position where they may be performing repair and replacement to viable sections of tunnel based on the original design life, while compromised sections of tunnel go unrepaired because of a lack of information.
Underwater Laser Scanning
The city elected to use an Inuktun Versatrax 300 crawler fitted with a 2G Robotics’ ULS-200 underwater laser scanner and a camera for the inspection. While the camera was used to capture video over the entire length of the tunnel, the ULS-200 was used to take scans at regular intervals. These scans produced a 3D model of the internal wall of the tunnel with millimetre level resolution. Unlike traditional single profile scanners, the position and orientation of the scanner head relative to the tunnel did not have to be controlled in order to acquire accurate measurements. Since the ULS-200 obtains complete swaths of data, the data can be digitally rotated to view the true tunnel profile.
The goal of this inspection was to measure small features and variations in the tunnel geometry over its length. Traditional video inspection does not obtain measurement data and sonar only provides rough overall shape information. By using the ULS-200 to obtain dimensional information about specific features, such as cracks and deformations, an engineering evaluation was done to determine if these defects are of concern and what remedial actions, if any, should be taken.
Highly Detailed Results
The ULS-200 created both localized fine detail measurements, as well as provided an overall picture of the geometry of the entire tunnel. This provided the City of Bellingham with high resolution geometric information about their raw water intake. Based on this information, the city now has baseline geometric data that can be used to assess with mm resolution how aspects of the tunnel geometry change over time. In particular, the regions where small but potentially critical changes to the overall shape of the tunnel occur will be of particular interest on future inspections. This ability to retroactively compare features of interest is only possible because 2G Robotics’ ULS-200 provides a comprehensive model of the tunnel in its current state.