Culvert/Storm Drain Evaluation Technologies
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2024-04-01
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Edition:Final Report Nov 2022 to Feb 2024
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Abstract:While LiDAR (light detection and ranging) is not a new technology to UDOT, mobile LiDAR has not been used to enhance culvert inspections. The study reviewed two types of mobile scanning technologies for testing culverts, Pocket LiDAR (iPhone 12 Pro based laser emitter that is used to improve accuracy of photogrammetry) and SLAM LiDAR (simultaneous location and mapping). The control was made with hand measurements or with Terrestrial LiDAR (which is a portable unit that scans an area with multiple static scans, similar to what UDOT uses for some of its surveying). This testing was performed to see if new versions of LiDAR could be used to supplement and improve culvert inspections within the scope of UDOT’s rating criteria. UDOT had an overall goal to be able to automate inspections so that a culvert inspection expert did not have to watch the video after the inspection to evaluate each defect that was found in a pipe. Culvert inspections offer challenges that are atypical to Terrestrial LiDAR surveying. While Terrestrial LiDAR had a lot of utility for its ability to gather large amounts of point cloud data from a distance with outdoor lighting, LiDAR in culverts is done over very small distances and with artificial lighting. Finding appropriate testing culverts that were easy and safe to enter with varied pipe materials was a challenge as many of the larger culverts that could be walked through are not readily accessible. This is often due to traffic safety issues with locations along state highways, water within the pipe or with locations where entry is limited due to structures. By coordinating with two groups that specialized in mobile LiDAR and determining a reasonable sample size that could be accomplished in two days, a group of 11 pipes was set. These pipes were: concrete, plastic and metal pipe types; had different diameters; were near enough that travel time was not a drain on resources; large enough for walk-thru mobile scanning; and the pipes exhibited varied defects. The testing found that the mobile technologies did well with some aspects of pipe measurements, including diameter, deflection, grade and joint gaps. The current measurement refinement level of this technology does not allow for meeting the UDOT inspection criteria for smaller defects such as fractures, surface deterioration, localized buckling, corrosion, and infiltration/exfiltration.
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