Consequences of a Deflected Pipe?
Consequences of a Deflected Pipe?
(OP)
A developer recently installed a new section of sanitary sewer in our City. On one segment of 8-inch PVC sewer (8-feet deep), the pipe has failed a deflection test (5% mandrel gets stuck). We televised the pipe and it looks good, other than a few scratches due to repeated mandrel pulling attempts (including the use of a vibrating mandrel, which would only go through while vibrating).
My questions/concerns include:
What are the long term consequences of accepting a deflected pipe such as this?
How much service life could be lost due to the deflection?
Are scratches on the inside pipe walls a concern?
Any comments or opinions are appreciated!
My questions/concerns include:
What are the long term consequences of accepting a deflected pipe such as this?
How much service life could be lost due to the deflection?
Are scratches on the inside pipe walls a concern?
Any comments or opinions are appreciated!





RE: Consequences of a Deflected Pipe?
Excessive deflection affects the pipe’s hydraulic performance such as decreased flow velocity and sediment deposition; but it may lead to harmful strain levels in the pipe wall that can trigger structural failure modes such as cracking, inverse curvature, and wall buckling. Excessive deflection may also compromise the pipe joint performance which can lead to exfiltration or infiltration, and the loss of backfill material causing sinkholes.
The deflection indicates that something was done incorrectly in the installation and should be repaired.
RE: Consequences of a Deflected Pipe?
RE: Consequences of a Deflected Pipe?
RE: Consequences of a Deflected Pipe?
The flowline of this pipe appears to be unaffected, not sagging.
This sewer is presently a dead-end/'start' line with very little potential for extension, so I am not concerned about capacity.
If anyone knows of a good spec that addresses requirements or steps-to-take due to a failed mandrel test I would enjoy reading this.
RE: Consequences of a Deflected Pipe?
RE: Consequences of a Deflected Pipe?
RE: Consequences of a Deflected Pipe?
RE: Consequences of a Deflected Pipe?
While I guess I should let the presentation speak for itself, it also explains that various different types of pipe that might be "substituted" are not equal in their interactions with the soil, and maintaining their shape etc in practical circumstances (as perhaps some might think, or wont). The Engineer should take a very active role to assure a good installation. See the very last/summary slide 53:
"Engineers design, specify, require and ENFORCE
The Engineer has a sworn duty to protect the public
health safety and welfare
Forgetting any of the above results in the Engineers
assuming the role of the Responsible Party with all
the risk, liability and consequences thereto."
RE: Consequences of a Deflected Pipe?
RE: Consequences of a Deflected Pipe?
RE: Consequences of a Deflected Pipe?
The thing needed to give consideration to are not only deflection but strain, stress, combined loading and buckling. Being a flexible the soil embedment and native soil properties are important as they provides a composite structure.
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