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Page 3 of 9 <br />North Fork Farmers Ditch Culvert Inspection <br /> <br /> <br /> <br />Shape 3 Poor with extreme deflection at isolated <br />locations, flattening of crown, crown radius <br />Horizontal Diameter 6 ≤10 percent of design <br />Seam and Joints 3 3-inch-long cracks at bolt holes on one seam <br />Metal Condition 3 Heavy rust, deep pitting, scattered perforations <br /> <br />Each of the criteria is rated on a scale of 1 to 10. The average rating for this culvert is 3.75, indicating the <br />need to examine remediation or replacement measures in the near future. <br /> <br />Opinion of Condition <br />Most state highway agencies factor in hydraulic capacity, structural capacity, traffic volume, height of fill, <br />remaining service life, and risk assessment (i.e., probability of failure and severity of consequences) when <br />rating the lifespan of a culvert. <br /> <br />In the case of this culvert, due to its length and land uses above it, the most deteriorated section of pipe <br />will control its serviceable life, but may not be indicative of the entire length. We can say that the <br />western third of the culvert, which is partially under a roadway, is in very good condition and has an <br />expected lifespan of probably 30 more years. <br /> <br />The middle third into part of the eastern third of the culvert has settled significantly and deformed as a <br />result of decay due to the presence of standing water. A normal outcome of metal culvert pipe corrosion <br />that has produced perforation is undermining (i.e., the formation of erosion voids in the embedment soil <br />below and beside the structure). These voids, typically adjacent to severe corrosion, are due to ingress of <br />water through the corroded zones and infiltration of backfill material under hydrostatic pressure. <br />Undermining results in a loss of soil support for the culvert. Without an adequate soil envelope around <br />the pipe, metal culverts have relatively little bending stiffness and are likely to deflect and exhibit shape <br />distortion or sags and joint opening.1 <br /> <br />Based on the FHWA condition matrix above, the load rating of the most deteriorated section of pipe, and <br />the degree of failure, it is our opinion that this culvert has approximately 3 to 7 years of life remaining. <br />Beyond that timeframe, the culvert will likely require replacement of deteriorated sections, or re-lining <br />using trenchless technologies such as cast-in-place pipe, or pipe bursting and re-lining with concrete, or <br />another section of smaller corrugated metal pipe to be inserted. <br /> <br />This concludes our report on this culvert. Should you have any questions regarding the information <br />presented herein, please do not hesitate to contact me anytime during business hours. <br /> <br />Sincerely, <br /> Jeff Ruppert, P.E. <br />Principal <br /> <br />1 Decision Analysis Guide for Corrugated Metal Culvert Rehabilitation and Replacement Using Trenchless <br />Technology, USDA Forest Service, December 2012.