Page 19 - Demo

COUNTY COMMENT %u2022 November 2024 19continuedBuried flexible culverts like metal and plastic pipes derive much of their structural integrity from the surrounding soil. The shape of buried pipes should be closely checked to determine if the soil/structure interface is functioning properly. Check for distortions from the original shape of the pipe. Metal pipes should be checked for corrosion, a common cause of failure in metal pipe culverts. All pipes should be checked for misalignments and faulty joint connections.The hydraulic performance of the culvert should be assessed during the inspection. The inspector should look for signs of overtopping, high water marks, and erosion and scour at culvert inlets and outlets. Undermining foundations on a span culvert is a major cause of culvert failure. The inspector should probe around foundations to detect signs of undermining. The channel should also be assessed since channel instability (incision, head cutting and alignment changes) can seriously affect the functionality and life of culverts.Figure 3. An extreme case of metal pipe distortion under the high fill of this busy road.Kansas LTAP offers an on-demand class on culvert inspections, which includes far more detailed information than what%u2019s included in this article. To schedule a class, contact Megan Hazelwood at mhazelwood@ku.edu.What rating scale should be used?The AASHTO Culvert and Storm Drain System Inspection Guide suggests a 1 through 4 rating scale for each culvert component. The scale shown in Figure 5 is for rating the condition of the culvert barrel. They provide the same scale with different descriptions for culvert components including the roadway, embankment, channel, end treatments, barrel alignment, barrel condition, joints, and seams.I prefer using a scale from 9 (new condition) to 1 (failed condition) similar to the one used for bridge condition ratings. On that scale, culverts or culvert components in good condition would be rated 7 or higher, those in fair condition are rated 5 or 6, and those in poor condition are rated 4 or lower. As opposed to the AASHTO rating system shown in Figure 5, inspectors and road managers are familiar with the scale used for bridge condition ratings. It also provides for degrees of good, fair, or poor ratings. A rating scale of 1-9 better answers the questions %u201chow good?%u201d or %u201chow poor?%u201d. This scale can be used for both span culverts and culverts under fill. The AASHTO rating scale is geared towards culverts under fill, not span culverts. Regardless of the scale used for culvert condition ratings, the important thing is getting out and inspecting those culverts. Even a simple culvert condition rating scale of good, fair, or poor, along Figure 4. Structural failure due to undermined foundation.