Pipe Connection to Manhole

[cher122976]

We have a proposed situation where we have a 18" perforated pipe at a depth of 12' and then a 36" storm drain directly above it at a depth of 5'. Due to proposed site conditions there is not a way to not have the pipes in this orientation.

Does anyone have ideas of how to connect these to a proposed 72" manhole? The one way I am thinking is to use an inside drop structure for the 36" connection.

Thanks

 

[bimr]

Not really sure what your concerns are.

Outside drop manholes are typically preferred. A drop pipe is typically specified for a sewer entering a sanitary manhole at an elevation of 24 inches or more above the manhole invert. Some jurisdictions allow storm sewers to enter with higher drops.

Inside drop connections are secured to the interior wall of the manhole and provide access for cleaning.

Due to the unequal earth pressures that would result from the backfilling operation in the vicinity of the manhole, the entire outside drop connection shall be encased in concrete.

Probably the best option is to use an outside drop for the 36-Inch and have the 36-Inch enter the manhole just above the 18-Inch.

In any case, you will have to have the approval of the local agency having jursidiction.

You will have to backfill with aggregrate. Due to the unequal earth pressures that would result from the backfilling operation in the vicinity of the manhole, the entire outside drop connection should be encased in concrete.

Here is a link to some examples:

http://old.lehi-ut.gov/userfiles/Sewer_Drain-SD.pdf

 

[dicksewerrat]

What is the perforated pipe draining? And Why? I'd expose the 36, take it out of service, then sink a manhole down to the 18. Doghouse the manhole as you get to the 18. Place a concrete slab under the manhole. Come back up to the 36, build a nappe curve and place a short MH section, top slab and MH ring and cover.

Richard A. Cornelius, P.E.

http://WWW.amlinereast.com

 

[gbam]

Sounds like you are out of the range of a standard manhole. Why not design a stormwater vault with an access hole. If your standard manhole riser is 4 or 5 feet in diameter the 36 inch is too wide to make a typical connection to the riser. Our standard is inside diameter of riser must be at least twice the outside diameter of the stormdrain pipe.

 

[dicksewerrat]

84 inch mh risers. Should be cheaper than reinforced concrete vault

Richard A. Cornelius, P.E.

http://WWW.amlinereast.com