Installation Cost of PE Pipe for a Gravity Sewer 3

[civilguy123]

I am currently working on the sewer line layout for an 80 acre residential development in South Louisiana and am looking into specifying P.E. 3408 pipe instead of PVC. The architect who did the site layout went with a "Cove" design, so there are winding roads throughout. Using PVC, I came up with a very large quantity of manholes that would be required due to changes in direction throughout the development. To make matters worse, the parish does not allow sewer manholes within the street, so I am forced to work with about 12' between the road and edge of the ROW where these manholes can be placed. I'm thinking with the P.E. pipe I can reduce the number of manholes considerably. However, the cost estimating software I have only has material and labor costs (no equipment costs) for P.E. pipe, and it's actually lower per foot than the cost to install PVC. Does anyone have a general rule of thumb as to how much P.E. pipe costs per linear foot installed? This will be the driving force in specifying the type of pipe to use.


Thanks in advance.

 

[Pinwards]

I typically check local agency (City, County, DOT, etc.) websites for any that post their bid tabulations, with the breakdown of unit costs. That way you can see a variety of prices and get a good average/median price for real projects in that vicinity. Just make sure you include bedding/backfill if those are separate line items.

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[bimr]

Are you referring to a pressure sewer system?

 

[civilguy123]

Pinwards, thanks for the post.

bimr, it will be a gravity sewer.

 

[bimr]

How is it that fewer manholes are needed for the PE pipe? Are not both the PE and PVC straight pipes and 8-Inch diameter?

Other than the cost difference for the materials, one would expect the installation cost would be similar.

 

[dicksewerrat]

He is going to fuse many lengths together and trench along with some curves in the trench and roll the pipe in the trench.

Richard A. Cornelius, P.E.

http://WWW.amlinereast.com

 

[civilguy123]

Dicksewerrat, that's what I had in mind. However, we have never dealt with anything other than PVC for gravity sewers so I am a bit skeptical to specify the P.E. pipe. Has anyone ever used P.E. pipe for gravity sewers? If so, were there any issues with constructability? I did a little research and it sounds like it can be a nightmare to install if the contractor does not have much experience with it. Even if the cost per foot to install the P.E. is higher than PVC, I think I will come out way cheaper in regards to the number of manholes I'll need for the P.E. pipe.

 

[bimr]

Never heard of running a sewer in a curve. One of the reasons that sewers are straight if for cleaning purposes.

"In general, sewers 24 inches (600 mm) or less shall be laid with straight alignment between
manholes. Straight alignment shall be checked by either using a laser beam or lamping.

Curvilinear alignment of sewers larger than 24 inches (600 mm) may be considered on a case by case
basis provided compression joints are specified and ASTM or specific pipe manufacturers' maximum
allowable pipe joint deflection limits are not exceeded. Curvilinear sewers shall be limited to
simple curves that start and end at manholes. When curvilinear sewers are proposed, the
recommended minimum slopes indicated in Paragraph 33.41 shall be increased accordingly to provide a
minimum velocity of 2.0 feet per second (0.6 m/s) when flowing full."

http://10statesstandards.com/wastewaterstandards.pdf

The local sewer agency would have to accept the piping material. If I was in their place, I would not accept it as it is too flexible.

To avoid wasting your time, you should run these questions by the local sewer agency.

 

[racookpe1978]

Can you really assume good, smooth interior surfaces of the pipe when it is cut and chamfered on-site (locally in the dirt and debris!) in the trench that many times? Seems that you're building in joints that will trap muck and waste at every chamfer.

 

[rconner]

Manholes are of course located/spaced for many reasons and also perform multiple system functions other than simply allowing for changes in direction or connection of sewer lines, with little or no relevance to type of pipe. Manhole spacing does indeed vary say from 300-500 feet in small collection systems, but most often spacing reflects available sewer maintenance methods and condition assessment practices (and in some cases also standards and/or regulatory requirements). While various plastic pipes with relatively low stiffness can of course be chosen for sewer pipes, and many types of pipes can be laid with deflection, sewers of any material are best when installed straight and furthermore the designer should however also be aware that with very low long term beam stiffness that when the prepared grade (or inspection) in installation is locally imperfect, the line once backfilled/loaded can basically conform to that imperfect grade, creating profile undulations and increasing the potential for "sag", ponding, and related gravity serviceability issues (may be exacerbated by high groundwater conditions as well). It should also be understood that any butt fused-type pipes will have a internal "bead" at every joint (unless same are required to be somehow removed by the installer) see the attached photo or depiction in patent

http://www.google.com/patents/US817...MrmJ4qQ9QTp84HQAw#v=onepage&q=8178640&f=false

) that protrudes into the flow.

 

[nackra]

Check OSHA requirements for soil classification(s). I suspect that gravity sewer depths will require benching or a protective system that may prevent rolling a pipe into a trench while maintaining required uniform slope

 

[Spartan5]

Other issues aside, the internal "bead" at every joint in butt fused-type PE pipes is readily removed with commonly available tools. See the depiction in patent

http://www.google.com/patents/US7422399

or at a random manufacturer's website

http://secoronline.com/product-categories/internal-bead-trimmer-tools/

The additional effort and labor required to remove the internal beads is minimal.

https://www.youtube.com/watch?v=z5URrLFKCR0

 

[dicksewerrat]

not matter what material you spec, the inexperienced contractor will make a mess of the project. You will have to make sure you follow the pipe manufacturers advice on the radius of the bending you put on the pipe. Don't try to shorten that radius just to save a manhole. You may kink the pipe. Design to pipe so you have less than 5% deflection on the pipe . If design says you need a SDR 25, use SDR 25. I would take out the internal portion of the "fusing bead" . Do not do any angle cuts on the pipe. Straight fusing only. And as BIMR said, Check with the local authorities before construction.

Richard A. Cornelius, P.E.

http://WWW.amlinereast.com

 

[civilguy123]

Thank you all for your responses. After speaking with Public Works, and talking it over with my principal, we will go with straight runs of PVC. Although I found some PVC manufacturers online with adequate bending radii in relation to the bending of the proposed streets, it won't be worth the problems we will probably run into in the field for construction. Also, as bimr pointed out, if we do a curvilinear design I will have to increase slopes. If that were the case, I would need to add another lift station, which would be very expensive. So we will go with "ole faithful" on this one.