Buried Water Tank

You may already have done a Google search on "external pressure on buried tank." The first hit is this very CR4 thread, so that's not too promising just yet. I looked at a few of the other articles without finding much.

One phenomenon you may soon come across is seismic fluidization. For that case, the pressure would be proportional to the depth and density of the soil (or rocks etc.)

That is a fairly severe case, but not necessarily the worst. Solid chunks in confined spaces can form bridges or arches with surprisingly high horizontal forces at the ends. This can happen in grain elevators, for instance.

Thanks for your input. I presume Rankine theory for lateral earth pressure could be used in this case..

EEUMA 190:2000

https://infostore.saiglobal.com/en-us/Standards/EEMUA-190-2000-494361_SAIG_EEMUA_EEMUA_1106461/

https://cr4.globalspec.com/thread/30700/Soil-Pressure-on-Buried-Vessel

https://www.eng-tips.com/viewthread.cfm?qid=295427

..."The pressure exerted by the earth is complex. The vertical pressure in undisturbed earth is the depth (H) multiplied by the density of the earth (d). However the lateral pressure (acting sideways) is a complicated matter. Usually the lateral pressure is usually less than the vertical pressure. The relationship between the vertical pressure and the lateral pressure is given by the Rankine formula. If you got to the website: http://www.dot.ca.gov/hq/esc/construction/Manuals/TrenchingandShoring/ch4_earth.pdf, you can get information on this.

The point of this is that a buried pressure vessel is subjected to a varying vertical pressure, and a varying lateral pressure which makes determining the stresses in the shell somewhat complicated. However, if the worst pressure, say at the bottom of the vessel were considered as an external pressure, you could probably safely design the vessel.
It is common practice to bury fuel tank in the ground, and that has a modest wall thickness. Often, a tank of 2000 mm diameter and 6 mm wall thickness will not collapse... provided it is not buried too deeply."...

http://forums.coade.com/ubbthreads/ubbthreads.php?ubb=showflat&Number=7313

https://www.eng-tips.com/viewthread.cfm?qid=295018

<...Often, a tank of 2000 mm diameter and 6 mm wall thickness will not collapse... provided it is not buried too deeply."...>

The truth of that would depend upon the materials of construction of the tank. The statement would not be true were it to be constructed in engineering brick, for example, or in reinforced concrete, which would be more likely than metals were the <...water...> destined for a potable application.

Thanks for your comment..

It would be strange for an organisation to not have a protocol for doing this, as it wouldn't be the first time a <...buried vertical tank- depth 6m...> has been designed. Some fundamentals:

• One must look at the bulk density of the medium in which it is <...buried...>, assume it is all liquid and the tank fully immersed in this medium, and do a calculation on that basis to ensure the structure is suitably strong enough to withstand the external forces.
• One must also look at the potential buoyancy of the <...tank...> and ensure that, at that bulk density and the <...tank...> empty and knowing its weight, the thing doesn't behave like a boat, and potentially float away.

The rest, being detailed design, is beyond the scope of the original posting.

The pressure acting at any depth is the product of the depth, the density of the material and the acceleration due to gravity, assuming that Physics textbooks haven't changed since 1971...

I'm picking nits, but that is not completely so. At low depths lateral pressure can exceed vertical pressure due to stress relief by erosion. To make an absurd example, If I sandpapered Everest down to nothing the state of stress induced by it's existence would persist leaving stresses greater in the horizontal planethan the vertical.. That's a little extreme for the stated question, but lack of specification makes it nit-picking-worthy.

Minor digression, but I once had to explain to an elderly lady what a septic tank (awaiting positioning on a housing project)) was. "So do they build some sort of steps so they can get up to the toilet?" she asked. Somehow I resisted answering in the affirmative and that a handrail would be added for safety.

That's some <...sandpaper...>!

That's why there are construction codes for all this sort of thing that a Designer would do well to follow: they make life so much easier.

<...buried...tank...> One could always partly-submerge a cast iron bath instead, perhaps.

Fixing two tubs together would be perfect. Drain and fill holes already in place.....I'll suggest it to sanit(ar)y director at KrisDel (export division).

Give some more information

• hypersensitivity potable water?
• Tank materials (which you already asked for)
• volume
• depth

there may be tanks already on the market...

"My precious!"

We be nice to them if they be nice to us!

Just to clarify, is it the tank high-point, center-line, or low point to be 6m deep, at what inside diameter?

Or, is the tank to be 6 m tall, at what inside diameter?

Why is the inside diameter of any special interest?

Because it affects the structure of the tank, which affects its weight and buoyancy.

...and, ultimately, the final project cost...

It is the effect of <...the...cost...> that is of interest.

Thank you all for your inputs.. I would use Rankine's theory in Soil Mechanics to solve this.

Then why did you ask the question in the first place?

You could check with Petroleum Companies/Engineers they bury there fuel storage tanks all the time. Every Gas station around here has at least two tanks in the ground.

You might think this off-topic- but for practical reasons when doing the work, make sure the tank is tied down securely - because, (if or instance it is to be buried in concrete) - you could come back the next day to find it had 'floated' to the surface - and in now sat on solid concrete!

Good point and You’re correct, also not off topic.

Ive seen septic tanks to that, where they had to pour a concrete slab over it.

How about providing a fully-dimensioned, top-front-side-isometric, drawing of what you actually are trying to do, and a capacity number to clarify the (ballpark?) size you want to install ? (...along with relevant geotech report data that accurately describes the ground you want to ''do'' it in?...)

A fully dimensioned drawing would only become available after detailed design is completed. The Original Poster is two steps upstream of that point.

It would appear that finding a Mentor at the facility who can carry out “second person check” on the design as it develops would be a valuable activity.

I like depth....and to rant. For example, the breadths and lengths to which this forum explains things is deep--very entertaining, stimulating. However, what we are really talking about here is the minimum structural integrity that would have to be designed into a tank buried at a predetermined depth, is it not? A spherical tank would be most efficient in terms of material used in proportion to volume, but likely the tank would be cylindrical.

So we're looking for a nominal value that excludes "acts of God" for liability purposes, in effect.. Are we marketing a product we wish to tout as being able to withstand extreme pressure without collapsing? Are we seeking to design a veritable bomb shelter? Or are we seeking the most cost-effective method of design?

Whatever pressures are being exerted by whichever variables instantaneously is pretty much a secondary consideration, don't you think? "Will the boat float and for how long" is the primary one. When it comes to sound design we'd likely need to attempt better reverse-engineering of the monolithic structures of pre-hustory, because the final derivative of the design would be how well it holds up to pressure over time.

Amen....

(G)ood (A)nswer, AND (G)ood (R)ant ?...

(...and, if no one bothers to tell an (enviro-obstructionist), then, maybe they''ll never know...?)