Culvert Type for Drainage Force Main

[Trackfiend]

Here's the situation. There is a lagoon that is capturing runoff from a particular site. The runoff from this lagoon is discharged in two ways, by (2)-48" gravity lines, and by (2)-36" force mains. Each of the gravity lines has a knife gate on the upstream end (in the lagoon portion). The gravity lines are kept open for nearly all rainfall events. During extremely intense rainfall events (hurricane), the gravity lines are closed and the pumps are used. After this new system was put into place, an 18' levee was constructed around the site. So all four lines (gravity and force main) run parallel to each other from the lagoon for roughly 300' (with 1.5' of cover) and then under a new levee, and dishcharge on the other side of the levee.

Recently, this new system was tested with a heavy rainfall and the pumps were used. The facility workers noticed that water was boiling up in certain spots and an outside consulting firm was brought in to investigate. It turns out that several of the pipes have cracks in them. The pipe material for the gravity lines is a corrugated plastic laminated metal. The pipe material for the force mains is what has me concerned. The pipes from the pumps start out as steel pipe, but once it gets underground, it transitions to PVC (specifically A2000 PVC). Strangely, the last 20' of discharge transitions back to steel.

My question is, what would be the benefit of using different material pipe and is this common? My first thought is that it is not and should not have been done. My role in this is to recheck this other firm's solution(s) to this problem and give advice.

BTW, per the specification for A2000 PVC, it is NOT suitable for pressure applications.

 

[cvg]

I know of agencies that do not allow HDPE or PVC at ends of larger culverts. The reason is fear that it may burn. At times, people enter the ends of these larger culverts and have been known to start fires which ignites the plastic pipe and it burns leaving an unsupported tunnel. The solution is to install steel or concrete pipe at the ends and begin the plastic pipe farther in where it is unlikely that anybody would set it on fire (accidently or on purpose).

 

[Rye1]

Find the design drawings and see what was spec'd. There could be some liability issues here.

 

[Trackfiend]

I have the design drawings from the original design and the drawings from the "redesign" which include fixing the problems by enhancing the pipe joints through internal couplings. The problems have been identified (cracks in the force main and gravity lines). I just don't understand the rationale behind transitioning between two different types of pipe material, especially for a force main. I would imagine one would have problems at the joints where these two different materials meet up.

cvg, that is quite interesting and I would have never thought of that in an initial design of a discharge pipe.

 

[dicksewerrat]

The contractor that built the new levee probably damaged the pipes and repiared with what he thought was good enough. Then added 18 feet of dirt surcharge. Find those inspection reports for the levee construction.

Richard A. Cornelius, P.E.

http://WWW.amlinereast.com