Concrete buried tanks Uplift check

[h-badawy]

Dear experts
In case of checking uplift on buried tanks have a heel (cantilever) footing should i take the uplift force equal to the column of water from ground water level till the bottom of the tank into full area of the footing or the displaced volume of water ,it gives to me big different values of uplift force and governed the quantity of concrete.


Thank you

 

[SgtYui]

In the case of buoyancy uplift only take into account the volume of displaced water acting on the tank.

 

[haynewp]

Displaced volume of water of the tanks and buried concrete.

 

[wannabeSE]

This link to an article on manhole flotation from the American Concrete Pipe Association may be useful:

http://www.concretepipe.org/wp-content/uploads/2014/09/DD_41.pdf

 

[oldestguy]

Something I didn't find in my quick review of the man hole article deals with anchors. Usually we figure the uplift resistance is the soil within the inverted truncated cone extending up from that toe slab at an angle from vertical of about 20 degrees for most soil. In most cases use the submerged unit weight of soil. Also of course the weight of the concrete.

 

[haynewp]

Does submerged soil really have that friction angle resistance?

 

[3DDave]

A story I love was of a buried chemical tank at a major research plant co-located with nice executive offices. The tank was placed in an open area near the research building and buried. A muckity-muck was going to give a tour and was not happy about the giant earth mound over the tank. He complained to the tank installation company who told him they would come back in a year to level the site. Impatient with that answer he contacted the lawn guys for the company who assured him that it would settle faster if there was water put on it. Since the tank was of significant size they tapped into the main water supply with fire-sized hoses and commenced to watering. After a short while the dirt was down a bit, so they continued for a while longer. Then the tank broke loose and heaved itself and its overburden of mud out of the hole, sending a wave over the lawn.

The tank was reburied and the mound untouched for a year. No word on the fate of the executive.

 

[h-badawy]

THANK YOU FOR ALL

Thank you

 

[Klitor]

Good question haynewp.

To follow up on it...

As a newbie I worked on some undg. valve chambers etc. for underground pipeline.

I couldnt make one particular (cca 5x5x4m) work with usual method (displaced volum VS concrete weight only) so my mentor at a time suggested I put 50cm cantilevers (nibs) in the bottom slab and use the truncated cone thing (10 degress...the soil was gravel IIRC so it was fi/3 angle).

Never had to use it again, but I wonder is this thing covered in any codes (never seen it in any geotech books i skimmed trough)? Are there any tables depending on soil type?