Storm Sewer under new building

[shorty]

I'm designing an industrial building expansion that will go over some existing storm sewer. Because of flow lines, I cannot route around the building. I was thinking of replacing the RCP pipe with steel (cast iron) and backfilling with cement stabalized sand to make sure it never moves.

Does anyone have any suggestions for putting storm sewer under a new building? It will be 24" ~ 150' long. Should I use some sort of restrained joint pipe?

 

[jboucher50]

Check your local building code and plumbing code first. You might not be allowed to run services under the building.

 

[CarlB]

I think you're on the right track as far as ensuring pipe never leaks. Use extra-thicker walled pipe. Restrained joints would be cheap extra "insurance". Use system other than tie-rods(they often corrode). May need to take some steps to ensure corrosion doesn't cause problems-at a minimum wrap with polyethlene "baggies".

 

[gibfrog]

Encase the 24" pipe in a 36" mild steel sleeve.

 

[hopk]

Ductile iron pipes encased in a concrete bedding ( 100mm all round the pipe )should be used to minimise any breakage due to sagging.

If possible, allowance to be made to provide a covered trench within the building just in case the pipe needs to be replaced.

 

[n3rei]

Depending how deep the pipe is, you may want to insure that the footing of the building is below the pipe or a sufficient cover is maintained between the bottom of footing and the top of pipe.

 

dumb idea.

you should never place a new building over a pipe:
what if the pipe collapses in the future!
what if you need to maitain that pipe!

Dumb idea,

relocate the pipe!

 

[carver]

I have had very similar instances where there was no opportunity to re route the pipe. I have spec'd DIP mechanical joint restrained pipe with a surrounding layer of open graded coarse drainage aggregate(gravel) with Amoco 4535 non-woven geotextile fabric. Hope this helps.

 

[PECPESC]

It is not a dumb idea. In some instances, you have no alternative. There are major storm drains under new bldgs. in downtown Dallas.

Best solution is the use a pipe casing (sleeve)large enough to allow a new storm drain pipe to be jacked thru. This will allow for replacement in the future if the new portion should ever fail. If the building has grade beams or curtain walls, make sure the structural guys leave a large enough opening for the casing (Min. of 6" clear) and that they span the opening with the bldg loads.

 

[bigot]

As a building drainage engineer, I have seen many sewers routed under new buildings where the re-routed cost was too prohibitive, in these cases the structure of the building over was "bridged" over the sewer, to ensure no load was added to the sewer.

The drain itself should be surrounded in a minimum of 150mm thick concrete, however it might be a good idea to allow a little movement via flexcell boards at each drain coupling, which breaks the concrete and allows a little flexibilty

 

[n3rei]

Hi!
Very good answers guys, especially the negative end of Mr.? waterflowsdownhill and the positive end in Mr.? bigot's crossing over discipline comments. It shows that sometimes all disclipines have to come together to solve a problem rationally. I liked the encasing comment of Mr.? WINhydro.
I belive that with this kind of starting comments you should be able to logically solve your problem. Make sure you talk to those structural and geotechnic guys also. This is not your everyday civil problem.

 

[dicksewerrat]

I'd think real hard about using a pipe twice as large as you need now. After 36 years with a local goverment sewer agency, twice as large is about proper. The original pipe was probably designed for a 2-5 year event. The new pipes they are installing at the upstream end of your pipe are 7-10 year event designs. Some day in the not to distant future, some Storm Water Manager will say" All the flooding is caused by_____________ building over our pipe and we can't up-size it." Then all hell breaks loose, law suits, etc. Putting in the upsized pipe now may cause a little sediment to build up in the pipe but a once a year cleaning will take care of that. And your building will be ready when the next wave of municipal improvments gets to your drainage area. also as others have said ,make sure the building is placing NO load on that pipe, now or 50 years from now.

 

[gibfrog]

I would like to expand upon my reply and comment about other suggestions
(1) Placing the pipe under a building is not optimal, but may be the lessor of all evils and most economical solution.
(2) The main considerations are leak proofing the pipe, replacing the pipe in the future and structual soundness. The commonly accepted solution is to sleeve the pipe, like in a "jack & bore" crossing. A 24" RCP pipe would propaply require a 36" mild steel sleeve because a minimum of 6" clearance around the bells is needed and a common standard size is usually cheapest. The sleeve prevents leaks under the building by moving them out side, usually 5' minimum beytound the footer, it also enables replacement of the carrier pipe and it usually is structually sound enough. You may want to check the loading at the footers and possible use a lintel over the pipe.
(3) Place the minimum size required by good design. Face it, storm water systems will always fail because a bigger than designed storm will sometimes occur. Just make sure that failure will not cause problematic flooding and remember that everywhere else will be flooded at the same time due to the downpour.
(4) Encasing the carrier pipe in concrete is not an optimum solution. It does not allow for pipe replacement and unless steel is used at all joints, it wil not prevet leakage. If any leakage should occur, the building will be endangered.
(5) If a larger pipe is needed in the future, then it will be "jack & bored" Clifford H Laubstein
FL Certified PE #58662