Partially buried AWWA water circular storage tank 1

[anthony gravagne]

Hello All:

I have a project that requires part of the external tank shell of a 50' diameter AWWA steel water tank to be partially below grade. The tank shell height is 14 feet and the users want to bury the tank 9 feet max into the ground. Any help on how to design the tank shell below grade would be greatly appreciated.

 

[LittleInch]

You might want to look up some military specs ad the are a lot of buried or semi buried tanks used for military fuel storage.

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[fel3]

For partial or complete burial of a water tank, I recommend concrete (either regularly reinforced or, preferably, prestressed) instead of steel. Steel, as you know, is very prone to corrosion and the coatings we apply don't last forever, especially in aggressive environments. It takes a lot more money, time, and effort to deal with underground corrosion compared to aboveground corrosion. Also, the thin steel plates would require require quite a bit of stiffening to handle the external soil pressures (you have to assume the tank will be empty at least once in a while).

But, if this tank must be steel, then I suggest talking to one of the bigger tank fabricators in your area. Perhaps they can provide you with construction details and calculations from a past project so you can see how it's done. Or perhaps they can put you in touch with their structural engineer (could be internal or a consultant).

I should point out that it is very common for the civil engineer to create a performance specification and some simple details for a water tank (my standard design requires three to four sheets), and leave the detailed structural design to the fabricator's engineer. For the tanks I have designed over the years, I reviewed the project with an in-house structural engineer, who then did some preliminary calcs to verify that the tank as a whole would work. He provided some input for the specifications and he reviewed our drawings. When it came to the fabricator's submittal, he and I both reviewed the fabricator's drawings and he reviewed the fabricator's engineer's calculations, which I only skimmed.

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"Is it the only lesson of history that mankind is unteachable?"
--Winston S. Churchill

 

[MJCronin]

Suggest that you post in the "Storage Tank Engineering" forum ... you will get lots of eyes there !!!

MJCronin
Sr. Process Engineer

 

[MotorCity]

I'm not sure if that is even permitted for a steel tank. It would make inspecting for leaks nearly impossible from only having access from the inside. In any case, one would need to check for the empty tank condition with only lateral soil pressure applied from the outside of the tank.

 

[HTURKAK]

I have seen this post a few days ago and could not get the explanation ' external tank shell'...Are there two shells one external and the other internal ?

Neither API 650 nor AWWA do not define buried tanks.. The scope of say AWWA , above ground or elevated tanks..

Typical buried or semi buried tanks are RC tanks and the design of shell based on the assumption that the wall ( with unit width ) is cantilever from bottom slab similar to retaining walls ..









I cannot give you the formula for success, but I can give you the formula for failure..It is: Try to please everybody.

 

[MJCronin]

Must the tank be partially buried because it spoils the view from some MBA's plush office ?

..... or perhaps because it presents a smaller military target ?

..... or perhaps some kind of bizzare zoning requirement in an excusive residential neighborhood ?

Whatever you do, make sure that you keep the reasons to yourself !!

Regards

MJCronin
Sr. Process Engineer

 

[JStephen]

The partially-buried tank CAN be done, but seldom is, for reasons pointed out above.
Buried steel tanks and buried steel pipelines have many of the same issues and both are common.
You do need to stiffen or thicken the shell for external pressure, and neither the loading nor the exact stiffening requirements are included in the tank standards.
Inspection for leaks is not really a consideration, but access for future maintenance is. Consider external cathodic systems also.
If a tank is buried on one side only (ie, built into a hill), consider a retainer wall on that side and keeping the tank entirely above-ground.
Also consider flotation of the whole tank if there is any possibility of ground water under the tank.

 

[LittleInch]

Anthony,

You need to log in and respond before we can go further.

So far you have posted 4 questions and not responded to any of them.

Semi buried tanks are possible and quite common for military fuel tanks but are not common elder so there are not good code examples. Extra thickness or strengthening will be required.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.