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Buried bends in storm drain piping

Buried bends in storm drain piping

(OP)
I am a PE currently working on a construction project. The project includes a length of buried drain piping shown on the drawings as being routed straight between two below grade structures. During installation, due to alleged unforeseen conditions, the contractor installed some of the work such that the remaining piping either needs to be installed through a manhole that is needed in order to achieve a turn or a 45-degree buried bend that would be needed for the same reason. The Contractor proposes the 45-degree bend. There is a concern that the bend may accumulate sand and gravel and therefore result in a clogged drain that is difficult to flush out or mechanically clean due to the bend.
In regards to whether or not 45 degree bends are technically permissible, this posting is intended to request insights regarding what: 1. industry standards apply, 2. what typical reference standards apply, 3. what technical requirements govern (e.g., Manning Equation).
Thank you for your thoughtful consideration.

RE: Buried bends in storm drain piping

no, either
a) install manhole
b) install clean out
c) re-align the drain

this is a maintenance issue not a standards issue. if this is a gravity drain, it will accumulate sediment and may also have trash or other debris that will get hung up or deposited at the bend. at some point the pipe will plug and cause flooding and the only way to clear it will be to dig and replace

contractors love to take these kind of shortcuts because they will be long gone by the time this drain plugs up

RE: Buried bends in storm drain piping

Whether or not there were unforeseen conditions, the contractor should not have freelanced the pipe alignment. The inspector (or Owner, depending on who has authority) should have stopped the work as soon as the freelancing was noticed.

Did unforeseen condition(s) actually exist that made the design on the plans unfeasible? If YES, then the contractor should have immediately brought this to the attention of the Owner's Rep, who should then have initiated a change order that included a redesign to deal with the unforeseen condition(s). If NO, then the contractor needs to rip it out and build it per the plans OR a deal could be worked out to keep what is acceptable, replace what isn't, and add one or more manholes as needed.

I once had a subcontractor freelance elevations (not alignments) for about a mile of sewer pipe on the site of a 5000-bed prison due to alleged but non-existent conflicts with other underground utilities. He didn't tell his prime contractor what he was doing, the State's inspectors never noticed (they never once checked a depth to invert with a simple tape measure), etc. It came to light when I saw the results of the record survey about a month after he was done laying and backfilling pipe. Fully half of the pipes were laid on adverse slopes and the rest were flatter than our design. We reran our sewer model and were able to accept about one quarter of the offending pipes, but the subcontractor got to reconstruct the other three-quarters of a mile.

==========
"Is it the only lesson of history that mankind is unteachable?"
--Winston S. Churchill

RE: Buried bends in storm drain piping

You need to drop a structure or rip the alignment out and start over. What is the pipe material? You can deflect RCP to an extent, but as was stated above, maintenance is going to be tough, and you're never going to know where that alignment actually is 20 years from now.

RE: Buried bends in storm drain piping

(OP)
The buried pipe material is ductile iron, with push on joints.

Thank you all for your very thoughtful/insightful responses (very touching actually). This experience and technical feedback sheds very helpful light on this situation.

RE: Buried bends in storm drain piping

I would have the manhole installed as well. Your pipe diameter could play an important roll in the systems performance as well. The smaller the diameter your using, the higher the chance for sediment accumulation you may have. Keep your pipe velocity at least 3 ft/sec or slightly higher. I just ran into a situation very similar to this last week. On our project it meant two more catch basins had to be purchased but in the long run that's cheap insurance knowing it was done correctly.

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