In today’s market there is more and more pressure to save money in construction. Owners are requesting products they have heard are cheaper. This puts design engineers in a very difficult position. To ensure the characteristics used in design exist following installation we recommend all thermoplastic pipe be installed according to AASHTO Section 30. This test ensures the plastic sleeve is installed correctly.
At the jobsite, all flexible pipe installation assurance should follow industry standards such as those laid out by The American Association of State Highway and Transportation Officials or AASHTO. Flexible pipe installation standards are addressed in Section 30 and state that the overall performance of the flexible pipe is highly dependent on installation handling, backfill material, and methods used to place and compact the backfill.
Plastic pipe is manufactured by a variety of methods and different profiles, but satisfactory performance of the culverts requires proper control of construction procedures at all times regardless of profile or manufacture method. Section 30 requires a mandrel test be performed a minimum of 30 days after installation once the pipe has settled. Mandrel testing, or deflection testing, is used to determine that the ovality of flexible sewer pipe meets design specification. This testing is critical to the long-term performance of PVC sewer lines being installed today. According to Section 30.7.2, if a mandrel is used for testing purposes, it shall be a nine (or greater odd number) arm mandrel and will be sized and inspected by the Engineer prior to testing. In locations where the pipe deflection exceeds 5% of the inside diameter the Contractor must have an evaluation performed by a Professional Engineer; all installed pipe deflections that exceed 5% of the inside diameter potentially indicate the installation was substandard. If the deflection exceeds 7.5% remediation or replacement of the pipe is required.
A result from deflection testing is to ensure the ability of flexible pipe to withstand soil load without exceeding maximum deflection limits. If the flexible pipe cannot withstand the soil load it could be directly related to the quality of the installation and compaction of the embedment material around the pipe.
With concrete pipe you have a single point of testing. Independently the DOT tests all pipe ensuring it meets the proper classification. It is not necessary to test and verify in the field every lineal foot of pipe backfill with concrete pipe as it is with a flexible sleeve. This greatly reduces the risk to the contractor and to the engineer. Give us a call at 605.528.3530 we would be glad to discuss any of our products with you.