Concrete Slab Inside Tank Has Bulged Up 1

[ansys54]

We have a 60' dia tank. From the base working up is a concrete base slab, welded steel tank bottom, 3' of granular fill and a 6" slab on a 30 degree incline toward the centre of the tank.

At approx. 17' out radially from the centre of the tank, the concrete slab has bulged up about 2'. It looks like a berm, gently sloping up and then back down. We cored holes and found the concrete slab has lifted leaving a void between the granular material and underside of slab.

Generally, the head of chemical in the tank is 12' above the elevation of the slab at the area in question.

Core samples showed a supersaturated granular material so we know the chemical is getting under the slab and being trapped by the steel tank liner below.

What could make the concrete heave up like this?

 

[JedClampett]

One off-the-wall reason I could think of is the chemical is reacting with the granular base and causing it to swell.

 

[VoyageofDiscovery]

Hi ansys54,

Has the density of the current chemical increased with regard to the design density? Has the head increased from the design head?

Does the tank foundation have a ring beam?

If this is the case, I suspect that the shell has buckled circumferentially.

Regards

VOD

 

[tomcrom]

If the head is 12' above the buckled area, and if the substance were water the pressure under the slab would be 12 x 62.4 = 745 #/sf. The concrete slab weighs .5 x 150 = 75 #/sf. If the tank is drained quickly, i.e. faster than the chemical can drain from underneath the slab the pressurized subbase will lift the slab. Pressure relief valves of some sort need to be installed and/or operators need to know how slowly to let the contents out of the tank.

 

[RDK]

Aggregate alkali reaction can cause swelling in the concrete.

Settlement of the ring beam could cause slab buckling.

Hydrostatic uplift due to rapid drawdown as described above.

What is the underlying base material? If clay is under the granular then the clay could have taken up moisture and swelled.

Two concrete slabs with a steel plate and granular material in between them?

Is the intent that the steel is the containment and that the granular material is the drainage layer? Which slab has heaved?

Do you know for sure if it’s heaving or settlement around the perimeter?



Rick Kitson MBA P.Eng

Construction Project Management
From conception to completion

http://www.kitsonengineering.com

 

[dik]

What sort of loads are on the exterior wall? Could it be that the large portion of the interior slab has a constant (more or less) moment that could give rise to the deformation?

What is the underlying soil?

2' is a pretty big deformation, thought... How big is the void?

 

[dirtsqueezer]

There is one possibility I don't see covered here. The volume of steel when rusted is much greater than it's original state. The '97 UBC specifies 3" concrete cover between steel and the subgrade. It might be worthwhile to check the steel in your cores to see if it's corroded.
Doesn't sound like fun either way. Best of luck.