does anyone know why you would need to use ductile iron pipe....

[dgi]

Does anyone know why you would need to use ductile iron pipe for sanitary sewer pipe where the storm is less than 2 feet at a crossing? A Town Engineer is requiring us to use dip with no transition manhole, just ferncos, to transition from pvc to dip and back again because the storm sewer is less than 2 feet away, even though the sanitary is lower than the storm.

Thx

dgi

 

[BobPE]

dgi:

that is pretty funny. Sounds like a well intentioned, clueless town engineer. I would hint to him that you are the design engineer and you wouldn't seal anything like that and that the town engineer will have to seal it. That usually stops them form making foolish design decisions like that.

Good luck

BobPE

 

[dgi]

Thanks for the quick response. You gave us a great idea, and the proper one too. Arguing does nothing but infuriate him, but making him sign might just stop the nonsense.

Thanks Bob

dgi

 

[dicksewerrat]

The Town engr. figures that bad compaction on the storm drain will cause it to settle and crush the sanitary. But no manholes ? Wonder why?

 

[EricC]

This sounds like the same requirements for sanitary sewers near watermains and this is done very frequently in that instance, so it may be difficult to justify not sealing it from that standpoint. The idea is to get joints (the weak part as far as leakage) away from the watermain.

While I've never heard of this requirement for storm sewer crossings, I do know that some in the industry believe that surcharing of a sanitary sewer will cause exfiltration of sanitary waste into the surrounding soil, and if the surcharge is greater than the ground water table, even push the wastewater "up" to storm sewers. Folks in New Orleans have been looking into it. It's the same reasoning as for watermain. Perhaps this town has had problems with sanitary waste showing up in the stormwater discharges, so they're being extra cautious.

We're not talking about big dollars here...you may want to reconsider how important your relationship with this town engineer is before going down the "you seal it" path.

 

[KRSServices]

One question, how are you proposing to effect the construction of the crossing?

Is the DI pipe is being requested at the crossing or does the proposed alignment of the sanitary run parallel to the storm line?

I believe I understand the town's rationale, but will reserve my opinion until my questions are answered, however I don't think that exfiltration has anything to do with it.

KRS Services

http://www.krs-services.com

 

[dgi]

The crossings are exactly parallel, he is asking for it in six places, lowest separation is 6 inches, highest is 1.8 feet, most storm are 12" RCP, with 8" HDPE sanitary. Ground is glacial till, very tight clay, water table at 12 feet.

dgi

 

[KRSServices]

You did not tell me how the pipe crossing is going to be constructed. I will assume the the excavation will be open cut.

While I haven't seen the crossing detail, I believe the engineer is concerned about the future integrity of the pvc due to the increased possibility of settlement and damage due to the weight of the storm pipe plus embankment combined with the effects of leaching stormwater (settlement or joint disruption during construction) into the surrounding soils, particularly the soils affecting the sanitary pipe. In the scheme of risk management, the more important pipe is the sanitary main, therefore, the ductile iron pipe is additional insurance due to it's increased strength.

The fernco coupler is an accepted method of transition, but I admit it might be tough to get the coupler to match the O.D. of the DI pipe relative to the SDR35.

As an alternate, you may want to ensure protection agaist settlement by providing sandbags (filled with sand/cement) to properly bridge the crossings. The 6" (vertical) crossing may be a bearcat, but it can be done. If you require a detail, I have a standard detail drawing that you could use, just change the title block. i know of some authorities that require a case bore under sensitive pipe or large diameter pipe to ensure the integrity of the pipes, as described above.

As a footnote, I have specified types of crossings such as these, and have had them recommended by engineers alike in their designs, so it is plausible that the Town Engineer and myself (or Consultants I have used) have crossed paths and shared "war" stories.

KRS Services

http://www.krs-services.com

 

[dicksewerrat]

Fernco makes all sizes of couplings from 2" and up and for most common pipe types. clay to PVC, PVC to DIP, DIP to Clay etc.

 

[dgi]

I'm sorry, I typed too fast and gave wrong info, the crossing are all perpendicular, sanitary below storm, open cut method.

dgi

 

[BobPE]

common guys, a fernco is not an acceptable device for this application....dgi was right to question that spec in his first post....ferncos may be alright for interior plumbing, but not for this application in a conveyance system. Dont get confused, engineers design conveyance, and we dont use ferncos for pvc-dip transitions in burried service. That is the funny part of the request made to dgi by the town engineer, protection of the pipes from inadequate clearance is a common issue all across the land...

BobPE

 

[KRSServices]

dgi, no worries, I assumed that perpendicular crossings were the case. You also confirmed my opinion regarding the D.I. pipe. I believe the main reason for the town engineer's stance is due to the methodology of the construction and likelihood of future problems due to compaction/settlement issues. The sandbag bridging will work well for some of the crossings enabling a possible relaxation of the D.I. requirement. He's only looking ahead about 20 or 30 years and doing his risk assessment and long term asset liability. I know there are other options that can be pursued and you should be able to provide some reasonable alternatives that will satisfy his objectives.

Bobpe, once again, I have to disagree with you. I have seen many design drawings and specifications (stamped and sealed by some very experienced engineers) specifying a variety of transition couplers (even Fernco couplers by name) on sanitary sewer mains, particularly replacements of pipe between manholes. In many of those cases they have been smaller diameter mains and service pipe (up to 16" I believe) and mostly clay to PVC or AC to PVC. Those couplers are also very common on sewer main and service repairs. Just ask any Public Works maintenance shop.

dicksewerrat, I guess it's never too late to learn something new, I did not realize that fernco has an adapter to D.I. Thank you for the clarification.

KRS Services

http://www.krs-services.com

 

[dgi]

I also should note for everyone, that this is virgin ground, used only for farming historically, being developed with a subdivision, not a preexisting condition or replacement of sanitary. Hope that clears up everyones understanding.

dgi

 

[BobPE]

dgi, go with your instict, its right, you do NOT put ferncos on new sewers...period...Use transition manholes if thats what you feel will give a 50 to 100 year design. That is what I would do. The additional cost is at the direction of the town engineer.

If an engineer shows a dip to pvc (or any other material) and I will add, on new construction, as in this case, without transition manholes, that engineer does not know what they are doing. I will not go into the reasons, since we are all engineers here?

BobPE

 

[dgi]

Thanks all for your comments, we have never had a request like this made on new construction before for sanitary/storm relations, thats why the question was asked.

dgi

 

[KRSServices]

I suppose everyone is entitled to their own opinions and design philosophies, that is why this forum succeeds.

New construction puts a different perspective on the question initially posed. Presuming the deeper main, in this case the sanitary line, would be first installation and the storm the second you should be able to effectively bridge the crossing without resorting to transitioning to D.I. at all as there really would be no need, unless there are other circimstances I am not aware of.

I am also presuming you are the design engineer for this development and/or subdivision and as such, your design is being reviewed by the Town for approval as a condition of the development agreement or subdivision servicing agreement. Getting back to your original question, yes, I believe I know why the Town Engineer requested the D.I. pipe. It's your design, if you are not in agreement with a change, it will be up to you to provide the rebuttal argument as to suitability of a transition or use of Fernco couplers, transition manholes or any other coupling system for the crossings or whether an alternate crossing option can be agreed upon. Agreement by the parties will allow the approval process to continue and the project moves forward.

Whether you agree or disagree with anyone's opinions here is really irrelevant. The threads posted to date clearly demonstrate differing opinions as to the method of transition, but ultimately, it really doesn't matter because you will ultimately choose an option you are most comfortable with. If you want manholes...use them, if you want couplers...specify them.

I personally think the whole request of transitioning from PVC to D.I. (or any other pipe type) is ridiculous and perhaps a tad inexperienced (within the context to which you have described), but nonetheless is a reality at this point. I also know what my reactions and recourse would be, as stated previously, but that is also a decision to which your firm, the Owner and the Town must resolve. I only know that my solution would not involve transitions, unless so ordered by the municipality and well documented on the drawings and in the design files and letters of correspondence.

KRS Services

http://www.krs-services.com

 

[dgi]

I will let you guys what we decide to do, KRS, do you have an email address so I can contact you? I'd like to review your details, this maybe a cost effective solution.

dgi

 

[KRSServices]

sure...

sobole@telusplanet.net

KRS Services

http://www.krs-services.com

 

[dicksewerrat]

If the sanitary sewer is along the centerline of the raodway, then the storm drain is crossing from curb to curb. Maybe a good place to place curb inlets and earase the 'fernco' problem. If it is not a low spot, design it in?

 

[fel3]

dgi…

I just happened upon this thread, so perhaps I'm a little late, but I wanted to point out something critical about using DIP for sewers: don't use the standard cement lining because the "nasty gasses" will eat it away, then attack the iron.

American Pipe makes a polyethylene lining for this purpose and other companies use polyurethane. I've never actually had either one installed, but I did have to spec DIP sewer once based on a client requirement, which I subsequently talked him out of.

Maybe you talk the town engineer into using a heavier wall PVC sewer or even PVC water pipe at the critical locations.

Fred