If there are septic tanks in a community, there can be shelters underground

[wercal]

31. Yoo-Hoo

I'm a civil engineer...and I drew the short straw so I also do small flows (residential septic).

You can weight down an empty tank - make the walls thicker, make the floor thicker, make the manhole riser taller, so more dirt is piled on the lid.

And its not necessarily the water pressure that can implode the tank, its the lateral earth pressure (which in clay soils is greatest when saturated).

But, similar to how a basement can withstand this pressure, so can tanks. Again, thicker walls, interior buttress, its all possible.

I do alot of elevated systems as you describe. They are usually because of shallow rock. If we encounter a high water table, we install a 'cutoff drain' around the perimeter...around 3 feet deep, and daylight it to the low side of the property. Just mounding up a system that drains to a shallow water table wouldn't be approved in my area...since the lateral field water would just leech out the side of the mound, if its really that wet.

All of the shelters in the OP look feasible to me, with a little planning and engineering.