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Gravity Sanitary Sewer Pipe Type Help

Gravity Sanitary Sewer Pipe Type Help

Gravity Sanitary Sewer Pipe Type Help

Hello everyone,
I've designed quite a bit of sewer, but it's all been pretty bland. I am looking at a new sewer main that will have 30 ft of cover, and on top of that railroad spurs. I've always used SDR 35 in the past, but could use some direction on the proper material for this application. The railroad people want something that will last forever so that their spurs don't have to be ripped up to fix or replace a sewer line.


RE: Gravity Sanitary Sewer Pipe Type Help

I'm surprised the RR didn't want a steel casing and then the pipe inside. At 30 feet deep the E-85 loading will not affect the pipe. However 30 feet of soil will. do the math and select the pipe that will withstand the dead load.

Richard A. Cornelius, P.E.

RE: Gravity Sanitary Sewer Pipe Type Help

They normally would require a casing, but in this case they're going to build a rail yard over the sewer after it is installed. So there could be 10 to 12 rail spurs built over the line, making it impractical to put the sewer line in a sleeve for that great a distance.

RE: Gravity Sanitary Sewer Pipe Type Help

Sorry, not E-85 should be E-80

Richard A. Cornelius, P.E.

RE: Gravity Sanitary Sewer Pipe Type Help

SDR-35 is to light for this application. I wouldn't go any thinner than SDR-21. Ductile Iron should also be considered. Include a proper bedding detail and enough inspection to make sure the installation is correct. With 30' of cover and railroad sidings on top, any failure or deformation will be a catastrophe. The additional cost of heavy pipe is small in comparison to the cost of failure

RE: Gravity Sanitary Sewer Pipe Type Help

Many people use a minimum of SDR-26 because the heavier sewer pipe is less likely to break when installing and less likely to deform during service. SDR-35 is probably not adequate for 35 feet burial depth.

You will have a Contract with the railroad. Follow what is in the Contract. Most railroads have standards for crossing rails too.

Casing may run several hundred feet, so your position on casing does not make sense.

RE: Gravity Sanitary Sewer Pipe Type Help

I did some calculations on depth for a project a few years ago. The transition from SDR35 to SDR26 was at about 30 feet. The pipe won't crack, but the ovalation gets near 5%.
The material is the same, PVC. PVC will have a very long service life if installed properly.
Use SDR26 (or 21) and make sure that your specs are correct for the compactive effort required. 100% construction observation should be required.
As bimr notes, it is not a bad idea to use SDR26 as a mminimum anyway due to constructability and handling. I had one site contractor tell me that they used SDR26 even if the plans called for SDR35 because the small additional cost was worth it.

RE: Gravity Sanitary Sewer Pipe Type Help

I've done work for a few municipalities that require all gravity sewer to be C-900/905. One uses DR-25, the other DR-18.

Make sure the railroad is on board with what ever you propose, but consider this: At 30' deep the cost of materials is realitively small. The cost of replacing a pipe below rails is quite significant. Dont skimp on the mateirals. If it's not cased, I'd consider DIP, bagged with HDPE & ceramic epoxy interior liner (Protecto 401 or similar). If they dont like DIP, C-900/905 DR-14 would be my second choice.

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