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Footings needed for tank pad?

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3467TXENGR

3467TXENGR

Civil/Environmental
Jun 24, 2014
1
I am designing a 14'x14' reinforced concrete pad to hold a 4000 gal water tank. I went through the design process for a one way slab and determined the slab thickness to be 12" thick with #6 bars at 12" spacing each way (top and bottom). Should I consider designing a grade beam at the edges or will a "floating" foundation be sufficient. My soil has a bearing capacity of 3,000 psf with a PI of 42. Any tips or considerations would be appreciated.
 
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Put down a thick mat of free draining crushed rock or gravel and let the slab float. Unless you are going to drive heavy equipment over the edge of the slab, at 12" thick, I would not worry about thickening the edge.

Mike McCann
MMC Engineering

 
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I would turn down the edges to get below the frost line if that is a concern in your area, otherwise, perimeter beams are not necessary.
 
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A clay with a PI of 42 is likely to be subject to volume change with seasonal moisture variation. I would consider whether there is the potential for differential swelling/shrinkage.
 
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Is there a concern if there is a little differential movement? After all, it is just a water tank, so perhaps it doesn't matter if it moves up or down seasonally provided the movement is within reason.

Using edge thickening to get below frost level doesn't help much as the middle portion will still be subject to frost heave.

BA
 
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Is the tank cylindrical? If so, can you enclose the foundation with a ring foundation and bear the tank walls on it and have the tank bottom bear on compacted soil within the ring foundation... done all the time in these environs.

Dik
 
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