September 2017 Vol. 25, No. 3

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Enhanced culvert inspections summarized in guidebook

culvert guidebook cover

A simple end-of-pipe visual inspection of culverts may not provide enough detail to manage culverts efficiently. To help users obtain additional detailed data, many inspection technologies have been developed. Which technology is right for the job? A new manual from MnDOT provides guidance.

The Enhanced Culvert Inspections Best Practices Guidebook is a primer on common culvert inspection technologies and applications. The manual summarizes the advantages and limitations of each technology and provides best practices when planning for and implementing an enhanced inspection project.

Enhanced inspection technologies can measure or digitally record conditions that would not be apparent from a simple visual inspection. Enhanced inspection methods include:

  • Laser profiling to measure precise culvert cross-section, dimensions, ovality, and holes
  • Sonar inspection to measure features below the water level
  • Inclinometer to measure culvert slope
  • Mandrel inspection to measure culvert cross-section and ovality verification
  • Hammer sound testing to identify voids within the wall of a concrete culvert
  • Core sampling to test compressive strength of the wall of a concrete culvert
  • Closed-circuit television (CCTV) camera inspection to obtain video documentation of culvert condition
  • Radio-operated camera inspection (e.g., Hydraulic Inspection Vehicle Explorer, HIVE) to obtain video documentation of culvert condition
  • JPEG mosaic (e.g., sidewall scanning) inspection to obtain a full digital image of a culvert’s interior surface

The report recommends balancing the higher cost of conducting an enhanced inspection against the quality of data needed. It is estimated that simple end-of-pipe visual inspection costs $0.07/ft. Enhanced inspections range from $0.23/ft. to $6.50/ ft., with higher-cost inspections providing more detailed data. Estimates are developed using year 2016 unit costs.

The best practices in the document were developed based on a combination of industry standards and MnDOT practice. In addition, the guidebook identifies practical and logistic considerations to assist staff in selecting cost-effective inspection methods for typical types of inspection.

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