partially burying a cistern not rated for burying

I fully expect this not to work. I'm looking at getting a ~3,000 gallon cistern. Our frost depth is 3 feet. The cistern very clearly says that it is not to be buried.  That said:

I know I could bury it in ~6" of dirt and it probably wouldn't make a difference. If I kept it full at the 3 foot depth then that would help a bit as well. But basically just curious if anyone has tried defying the manufacturer's recommendations with any success.

Is the purpose for burying this cistern strictly freeze protection, or do you have other goals as well?

What is the shape of the cistern, in detail? That will strongly influence how far it can safely be buried. We need to know that before we can give any sort of useful advice or guesses, even by someone who has done a similar thing. I am certain that it would not be able to stand burial under any kind of vehicle access. Freeze-thaw pressure would be another issue over time, unless the footprint is perfectly symmetrical and round.

Glenn,

It's really just for freeze protection. I'm looking at this unit in particular: https://www.ntotank.com/3000gallon-enduraplas-beige-vertical-water-tank-x3639663

I've seen someone say that the manufacturer says that you can bury them 3' but can't seem to get that from the manufacturer. I found an old youtube from someone in the cistern business who says you can bury it a bit, and the deeper/emptier you go the more you're gambling.  https://www.youtube.com/watch?v=WNLSPXAVzpU

So ideally, for me, for something like this that's ~8' feet tall, I'd want it sitting down 3', so 5' sticking up in the sunshine.

I'm not an expert, so keep that in mind.  If you kept the tank filled with water to above the soil line, I can't believe the soil could collapse it.  I think a lot depends on your soil as well. I have heavy clay that simply doesn't exert a lot of pressure sideways.  I can dig a hole three feet deep and it won't collapse in with nothing at all in the hole, so I'm sure I could bury that tank and not have a problem.  I would put a layer of sand under it so no rocks could poke into it, and probably do the same on the sides if it were feasible.  If you have nothing but sand and it can't hold it's form at all if you dig a hole, that might be a different story.  Again, I think if you filled the tank with water to the soil level first and then buried it, it would be fine.  All that said, I'm not an engineer, so if I were going to try it, I would make sure that if it did somehow collapse, there would be no danger to people or animals.

Trace, that's what I'm thinking too. And it gets worse as the tank gets emptier. Ie: 2.5 feet of water in a tank that's 3' buried isn't as bad as only 1 feet of water in the same tank, etc.

Offhand, I have this notion of digging a hole for the the cistern that is well below the frost line, to take advantage of natural earth heating. Then, stacking straw bales all around and above and tarping the whole shebang. No soil pressure on the tank itself, and lots of helpful heat from below. Might work?  

The pressure from soil is relentless, in my experience even shipping containers only buried with the floor 10 feet down have been crushed like an aluminium can in my hand.
underground tanks are spherical for a reason!