Wall Foundations Parallel to below ground plumbing lines 2

[Celt83]

5-story residential structure on grade, no basement. floor framing spans exterior to corridor.
we have a situation where due to the sanitary hookup outside the interior below grade lines are several feet below where we would normally place the foundations. How are people addressing this condition:
- drop the foundations to get below a 1:1 influence area of the pipe
- keep the foundations high and add notes in the contract documents to shore the structure when any maintenance is required for the below grade lines

If it were a single location perpendicular to the wall line I'd put a grade beam to span the area but these lines are parallel and match the length of the wall foundation.

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[GeoPaveTraffic]

You best place the foundations below the elevation of the utility lines. Not only will anything else be a problem for future maintenance, but do you really want to support a 5 story structure on the backfill placed and "compacted" by a utility contractor?

Mike Lambert

 

[Celt83]

GeoPaveTraffic:
That is usually what I would do but the height delta here is well beyond what we have seen in the past, used to it being 3-4' so cost impact of stepping the footing to match the 1/8" per foot pipe fall isn't to much. In this instance were talking about dropping the footings almost two stories into the dirt has significant cost impact. At that much extra height my gut says I need to look into the stability of the cast-in place stem wall as well.

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[LittleInch]

~Are you installing this pipe or is it there now?

If this isn't your pipe then you need to ask the utility / owner.
If it is your new pipe then just make it a bit stronger.

And hope you never have to dig it up again.

How big is the pipe / material?

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[phamENG]

What kind of pipe are we talking about? 4" pressurized water, or a large sewer pipe? If it's a pressurized pipe, I would be more concerned with the impact of a pipe failure on the surrounding soils and eroding a cavity beneath the footing. It's possible with a gravity drain pipe, too, but would likely occur more slowly. Maintenance of a sewer pipes can often be maintained from within - cleaning and even re-lining. It's not cheap, but also may not need to be done for 50+ years.

Given the depth, I wouldn't worry too much about maintenance. You would either need a 20' retaining wall on either side to facilitate that future maintenance, or they'll need to install braced cut shoring anyway.

 

[Celt83]

All new construction, site is being regraded to raise t/grade by about 20-22'.

It's a 6" pvc sanitary line, with multiple hook ups along the length from the residential unit stacks.

Screen Snip:
Grids 17 and 18 are the bearing wall lines total length of the bearing line is about 274'

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[phamENG]

Have you discussed future maintenance needs with the plumbing engineer? Given the potential cost impacts, it's probably worth it to get a good picture of the actual need to access it and advise the owner accordingly.

 

[oldestguy]

I assume your placing foundations on compacted ground means you have no problem with footing settling. The main question is the pipe of a class capable of carrying the soil pressure from that soil load above it. Likely with your dimensions the foundations will spread their loads out so no point loads, or similar, are on the pipe. If any problem, widen the footings and reduce the pressure up there.

 

[Celt83]

oldestguy:
correct based on the geotechnical recommendations should not be any settlement issues. There are several locations of concentrated post loads and shear wall chords but service level bearing pressure stays between 2600 and 3000 psf.

I have a few emails out to the plumbing engineer to try and get some clarification these inverts just got dropped on us this morning with a permit set due this afternoon.

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[jayrod12]

Why don't they have the pipe come straight upwards when it enters the building to a reasonable elevation and then begin it's horizontal run? Seems like it's maybe 2 more elbows and overall less pipe.

 

[Celt83]

yeah along with maintenance requirements that's one of the other things I've asked the plumbing engineer.

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[jayrod12]

Seems like it's a no-brainer. I can't see any reason to maintain that depth below the building for the entire line.