Bearing Pressure for Ring Wall Foundation 1

[sfinlayson]

I am designing a ringwall for a steel tank. The tank is 110 ft in diameter and 45 ft high, filled with liquid asphalt. I am trying to determine my bearing pressure below to size the ringwall width. I am assuming that the weight of liquid resting directly on the ground goes into the ground and the weight of liquid directly above the ringwall goes into the ringwall. Is this a reasonable assumption? Based on my weight and moment due to wind (controlling moment) and a bearing capacity limit of 2500 psf, I need a ringwall that is 3'9" wide. For those of you who have a lot of experience with this type of design, does this width sound reasonable?

 

[SlideRuleEra]

See the paper "Oil Tank Foundations - Boberg" at this page of my website

http://www.slideruleera.net/foundations.html

On projects with soft soils sometimes we would size ringwall thickness for hoop stress and construct it on a footing of the appropriate width to meet allowable soil bearing pressure.

Cost of the above approach versus a thick ringwall, like you have proposed, are probably about equal.

http://www.SlideRuleEra.net

 

[BigH]

Question - why do you need a concrete ring wall? - we have discussed this before. Most seem to be for it; I have never been involved in tanks where it has been done and these include tanks of some 200 ft in diameter or more.

 

[SlideRuleEra]

BigH - One reason why we use ring walls for tank foundations at electric generating stations has to with future maintenance, construction and system modifications. Tanks are often located in congested space near the plant island (turbine/generator/boiler area). There is an underground network of assorted piping and electrical ductbanks - much of it having nothing to do with the tanks themselves.

When the time comes to dig up these buried utilities a ring wall makes it possible to excavate immediately adjacent to the tank (often on short notice for piping or electrical failure) without concern that that the tank will be undermined.

http://www.SlideRuleEra.net

 

[BigH]

Okay - I can see your point, but at at least 3 refineries and a few large tank farms (300 ft dia tanks) of which I am familiar, we never did - we just put them on granular tank pad foundations. A renowned geotech in India that has designed over 1000 of them has also done the same thing. The point I make is - it makes sense when there is a valid reason for it - but not all cases require them and I would be hard pressed to put them in just because. Cheers

 

[sfinlayson]

In my case, this is a conceptual study where we are analyzing three options and presenting them to the client with the advantages and disadvantages of each option along with a cost estimate for each. The other two options would be a prepared surface without a ringwall, and a foundation reinforced with stone columns.

 

[BigH]

Perhaps we should know what the soils are that you are dealing with. Soft or firm clays? Or . . . ? I am surprised that you would go with stone columns unless your soils are quite poor. What is your undrained shear strengths? How thick of clay layer (I am presuming that this is what you have or you wouldn't be considering stone columns). We have successfully built on firm clays with large diameter tanks but "with care". Normally on a granular pad of some 5 ft thick extending 10 to 15 ft beyond the tank rim.