Driven pipe pile with uplift

[bhiggins]

Hi All!

I'm designing a pool foundation which consists of 8" diameter steel pipe piles, 12"X30" concrete grade beams spanning between piles which supports a pool shell. The pool is about 7' deep and there is a high water table so there will be net uplift from buoyancy forces. The typical detail is that the piles are filled with concrete and there are (2) #5 18"x72" hooks embeded in the piles which connect the piles to the grade beams. This is how I designed the house foundation which has no uplift, but is this a reliable way to resist uplift? Is there a mechanism for transferring load via bond or friction from the concrete to the pipe piles? I'm guessing I'll need something a little more robust, does anyone have any suggested details to take care of this situation? Maybe a upside-down baseplate with headed studs? Weld deformed bar anchors to the pipe column? Uplift is roughly 12k per pile.

Thanks!

 

[azcats]

My first thought was to weld the rebar to the outside of the pile like you suggest. Although this relies on the pile remaining free of deterioration forever. Piles galvanized?

I'd be tempted to use a really long rebar inside the pipe as well. Size the length based on a conservative estimate of bond. There are a few references to bond strength in this thread: thread507-212176

 

[oldestguy]

How's come you can't support, or at least have under the pool, a layer of single sized gravel and then a few one way valves in the base of the pool so that any high water table will active the valves to let water in? Is the pool "skin" capable of handling uplift from exterior uplift pressure, even if tied to those piles?

 

[Ron]

Obviously you only have a problem when the pool is dewatered. While your net uplift is likely there, assuming water table is at or above the pool water level, the piles should cover that and your connections need to be designed to accommodate that net uplift as it appears you have done; however, keep in mind that each pile location will result in a negative punching shear condition that you'll have to cover with your reinforcing.

Agree with OG that you could also have a fail-safe system in place for inadvertent dewatering of the pool.


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[bhiggins]

Thanks ya'll for your comments. As OG suggested, I just talked with the pool designer and they stated that they can install a hydrostatic relief valve to prevent a situation like this. I will still install welded deformed bar anchors to the piles just to be safe in case the relief valve fails or if they forget to install it. The slab is tied to grade beams so it has been designed to span both gravity and uplift conditions.