Concrete Tank Slab

[Kowycz]

I am currently revising a concrete clarifier slab thickness and reinforcement. The clarifier is being relocated on the site from a poor soil condition location to a relatively good soil condition location. We are in the process of getting new bore holes drilled in the exact location; however a couple bore holes were almost in this location from the original borings.

Tank dimensions:
Diam = 60'-0"
SWD = 12'-0"

My supervisor instructed me that he would just make the slab 2'0" thick and there really isn't any design involved save the bearing capacity of the soil and flotation calculations.

I was just interested in getting a second perspective on the situation.

Thanks

 

[SlideRuleEra]

You mention flotation. If flotation governs (compared to bearing), perhaps the dead weight of a 2' thick slab is needed to overcome flotation (even if 2' thick is more than enough for bearing). The correct answer depends on the details.

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[Kowycz]

You mention flotation. If flotation governs (compared to bearing), perhaps the dead weight of a 2' thick slab is needed to overcome flotation (even if 2' thick is more than enough for bearing). The correct answer depends on the details.

According to the flotation calculations 18" is the depth necessary. I was just wanting to ensure there wasn't something else I might be overlooking.

 

[JedClampett]

We make clarifier slabs as thin as 8 inches away from the thickened edges. Except at the walls, they pretty much just pass the liquid load right to subgrade. So 18 inches should be plenty thick.
We also like to put a 2 inch grout topping, placed by the clarifier mechanism. This provides a better tolerance for the sweeps. Other designers don't do this, so it's up to you. And I wouldn't count on this for flotation resistance.