Columns Adjacent to Swimming Pool

[XR250]

I have an Arch. who want to put some canopy columns 18" from a new proposed swimming pool. The columns will be the fulcrum for a 9 ft. cantilevered roof so they have a fair amount of up and down demand. Not so much lateral as the roof will be braced against a nearby garage. Any ideas on the type of foundation I should use? I am not involved in the pool design, but I would like an idea that won't be compromised by the pool and vice-versa.
They are not sure yet if it will be a vinyl lined or gunite pool. FWIW, the end of the pool is only 12' wide and the columns will be near the corners.

Thanks

 

[Lomarandil]

How deep is the pool? My immediate impulse is to go deep (drilled shaft?) if you want them to be independent.

----
The name is a long story -- just call me Lo.

 

[XR250]

Not sure if this is the deep of shallow end. I am waiting for some additional info. Maybe put this thread on hold til then. I was also thinking drilled piers although they are not very common around here in residential. If this is the shallow end, maybe just a deep concrete filled trench?

 

[XR250]

So it is a gunite pool and I am dealing with the deep end.

 

[JoshPlumSE]

Usually, pools are just designed as retaining walls. So, you could go with a spread footing and just add that in as a surcharge load on the retaining wall. Though, 18" is really close. Therefore, I would probably be more comfortable with a drilled pier as well.

 

[XR250]

Usually, pools are just designed as retaining walls

Most pools I see go in around here appear to be simply a web of rebar sprayed with gunite. I am not sure there is any design involved and they do not appear to be too thick.
I think a drilled pier may be the way to go.

 

[KootK]

Is there hardscape or something that could be relied upon to restrain the tops of the piers laterally?

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[bhugey]

A drilled pier would seem to require consideration of the pool being excavated out, removing lateral restraint for pier. Whatever the solution, would suggest that it has to go below pool as it would not be too surprising that a pool replacement would be needed in the future. Foundation needs to be designed for the conditions you can and cannot control.

 

[racookpe1978]

Further, you want to specify that the column foundation cannot be "connected" in any way to the pool wall or pool walkway (pool edge, its sidewalk and its splash tiles) around the pool. As the pool fills and empties from initial dig to gunite construction, final lining and painting, water fill and drain later, you don't want that movement of the pool and soil to be jerking the column up and down. It has to be separate concrete and separate rebar. As mentioned above, deeper than the pool.

Not sure though if the hole for the column can be drilled out and poured after the pool completes, probably not.

 

[EngineeringEric]

Id do deep augered CIP holes. my understanding from pool people is they cannot support any superimposed loads and they will cry foul if it cracks and you placed a column near it.

 

[Tmoose]

It sounds like most concerns are with the piers under the columns loading the pool wall via the soil.
I'm no civil engineer, but that would be my concern too.

While not exactly the same phenomenon, note how threaded threaded fasteners can distort a cast iron engine block a measureable amount.

http://www.grumpysperformance.com/torqueplt1.jpg

I wonder if a full length block of styrofoam etc 2 inches thick could be placed the full height of the pool wall in the vicinity of the column to decouple the pool wall from the column piers and footing effects.

I'm guessing no matter what, if in the future cracks develop anywhere near the column footings, there are probably mitigation steps you, not the pool company, will be required to provide. I'd be tempted to add some US bucks to my bill for that eventuality.

https://www.doityourself.com/stry/tips-for-repairing-a-gunite-swimming-pool

 

[KootK]

my understanding from pool people is they cannot support any superimposed loads and they will cry foul if it cracks and you placed a column near it.

Yeah, I'm pretty sure that the pool folks and the elevator people hang out socially. PDH conferences on how to maximize obstinacy etc.

Not so much lateral as the roof will be braced against a nearby garage.

I would like to see or hear about a cross section through the garage, pool, and these columns. I'd be surprised if your final decision on this wasn't significantly impacted by the proximity of various things, both vertically and horizontally. A combined foundation supporting both columns might make sense. There is a moment after all, it's just split into a couple, right?



I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[EngineeringEric]

Pool people, Elevator folk, and Move-able partition trolls who want zero vertical deflection on a 30ft span.

If you do a deeper foundation, i would still design the base of the column as a pin and not require the transfer of moment into the pedestal or foundation element. This will help ensure a more rigid (in rotation terms) connection where you are not imposing loads onto the pool walls.

 

[XR250]

Thanks for all of the insight. Here is plan view. After making some phone calls to some local excavators and the contractor, drilled piers may not be a viable option. i may just wait until the project gets further along and see if the me and the contractor and pool folks can coordinate and come up with a solution to keep everyone happy.

 

[azcats]

How about a long, deep trench footing connecting the two columns? Bottom of trench at or below the bottom of the pool? Could install that first and then excavate the pool later. If you really desired, you could foam the sides of the trench for some isolation.

 

[XR250]

How about a long, deep trench footing connecting the two columns? Bottom of trench at or below the bottom of the pool? Could install that first and then excavate the pool later. If you really desired, you could foam the sides of the trench for some isolation.

Seems like the pool excavation would likely expose the entire face of the trench footing which would end up connecting the two in the process. Also, the "footing" may simply tip over when this happens (unlikely since vertical cuts in the soil around here never seem to fail)

 

[azcats]

Yeah - crappy idea on my part.

Trench footings either end rotated 90° w/ a grade beam in between? Look like an I from a plan view.

 

[XR250]

Trench footings either end rotated 90° w/ a grade beam in between? Look like an I from a plan view.

Ah, much better.

 

[XR250]

.....but how to get in there to tie the rebar?

 

[azcats]

How deep is the grade beam?

Any way to tie the cages independently, drop them in the holes and finish shuffling ties or corner bars from the top?