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options for spread foundation settling/leaning on 1 side
2

options for spread foundation settling/leaning on 1 side

options for spread foundation settling/leaning on 1 side

(OP)
i have a pipeline support leaning/settling on 1 side. i think this is a spread footing based on the pic.
i'm not the original designer nor have i been to the site to check.

i'm thinking to wait if settling would stop, it still seems to be still supporting the pipeline.
if it continues then i'll replace it.

any options of preventing this foundation from settling further.

also shouldn't foundations really lean/settle a certain amount.
i only check soil bearing and assume settling would be ok if i meet soil bearing.

any ideas would be appreciated.

RE: options for spread foundation settling/leaning on 1 side

I can't tell anything from the picture really, but does it matter? Unless your math shows that the existing foundation is significantly over a reasonable allowable bearing capacity or there are stability issues, you might be able to fix it by shimming the pipe. You might have to do it a couple of times.

Also, vertical pipe supports often end up being spaced based on deflection criteria rather than stress. You've basically got a beam (the pipe) on spring foundations. If this one settles, load will shift away from it unless there's a large amount of flexibility in the piping system nearby. The fact that settlement stops doesn't mean that the support is actually functioning. It may mean that it's stopped settling because the load has all shifted elsewhere. The pipe /can't/ push the support down lower than the point it would settle to without the support, so you'll never see a gap open up (unless a cold case puts it under enough tension to pull some deflection out of it). Of course, this additional deflection and stress may or may not actually hurt the piping system.

Basically, what you have to do, and whether you even need to do it, is going to be heavily governed by the piping design.

RE: options for spread foundation settling/leaning on 1 side

Compunction grouting has been done to raise settled foundations. It takes a well experienced contractor. Do not consider using one who mud-jacks slabs, since control of the action in your case needs an expert who can work at depth.

RE: options for spread foundation settling/leaning on 1 side

(OP)
if you zoom closely there is a gap between pipe steel plate and concrete.
are there any grout that i can use fill the gap between plate and concrete.
is steel shim plate the only option to fill the gap.

piping required a support at that location so i will put a support or fix that support regardless whether the pipe can span without that support.

RE: options for spread foundation settling/leaning on 1 side

Since settlement is being monitored, suggest using temporary hardwood wedges until you have enough info to determine if support repair is practical or replacement becomes necessary. Use of temporary materials will preserve all options until an informed decision can be made.

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RE: options for spread foundation settling/leaning on 1 side

Assuming it's settlement, if it's settled to the point that there's a gap you've got a problem. If the pipe in that photo is full, then it should be near it's maximum deflection. If there's a gap at maximum deflection it means that the foundation may have settled under the selfweight of the footing alone. That's not a great sign. I'd expect that, once you make up the gap, you'd get even more settlement due to the operating weight of the pipe. Also, you can get a rough idea of the order of magnitude of the settlement by calculating the deflection of the pipe between the supports on either side of the support in question. It's obviously slightly more than that.

Honestly, even large pipe supports don't have a huge vertical loads on them compared to usual allowable ground pressures, nor does a plain footing. If anything, I tend to run into bearing pressure issues due to overturning from friction, but that type of failure doesn't really look like this. It also doesn't sound like you're having problems on the other supports. If this is a typical support, you'd expect other supports to act similarly if it were a systemic design problem. If you've had a reasonable amount of settlement in just this one spot it's likely due to poor ground prep, really bad ground conditions or something silly (installation on frozen ground). There could also be a systemic design problem, but it's likely something in combination with that if it is.

Alternately, it may have been installed with a screwed up elevation. Are you sure this is a new condition? As pipes get larger, the typical spacing is sometimes close enough together that your pipe won't always deflect to hit every support when they're built to standard construction tolerances. It's pretty common to have to come back and shim some supports in these cases.

Also, I'm assuming this pipe keeps going relatively straight and doesn't do anything like a hard vertical elbow that could result in liftoff in certain piping temperature cases.

My path forward would likely be to go and look at it and the adjacent supports to see if I could figure out what's going on. I'd also do the math to see what the bearing pressure looks like. What to do next depends on the timeline. If I wasn't sure of the cause and had some time, I'd start by having them shim the pipe the next time it's empty. Then watch over the next while to see if it settles more. If it does, then you get to do rehabilitation on the footing. That could be grouting, or excavating and extending the footing. You'll have a lot of flexibility in your methodology because the pipe obviously doesn't collapse when you remove the support. You won't have to maintain a load path during construction, which makes things much easier.

If you want to close the gap, steel shims are pretty typical for piping. You could use a bunch of different grouting techniques, though. If the gap gets really small, pressure grouting would work. Try not to inadvertently bond the shoe to the support, though.

(Sorry, this got a bit stream of consciousness on me)

RE: options for spread foundation settling/leaning on 1 side

Delagina:
I think SRE and TLHS have given you particularly good advice in their last two posts. Go slowly if you can and try to gain an understanding of what’s going on with the pipe support, and what’s causing the problem, what loads, what movements, etc. This will ultimately lead to a better solution and fix. I don’t think you know this right now. I would shim the gap btwn. the pipe and the support when the pipe is empty, so that you take pipe deflection out of the shimming process as much as possible. That is, maximize the gap to be shimmed, and the pipe loading after shimming if that is causing the support movement. I would also shoot some elevations on the four corners of the support and on the pipe over the support and at a couple equal distant points removed from the support. I would also take some horiz. control measurements to various points on the support and on the pipe, from control points unmoving and unrelated to the pipe and pipe support. You would like to see what’s moving and in which directions. If you can buy some time and really understand the problem, you almost always arrive at a better solution. Everyone else always wants quicker, and then be gone; that is, until the first guess didn’t do it, then it’s your fault, again.

RE: options for spread foundation settling/leaning on 1 side

Maybe add a couple of helical piers under the settled end.
Quick and cheap.

RE: options for spread foundation settling/leaning on 1 side

if shims are used, may be a good idea to check the concentrated local bearing loads on the pipe/saddle @ the shims....

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