Hey sklar, welcome to the forum. I like your ideas and have had some of them myself to some degree. I saw all those millions of pounds stacked on freight ships in container stacks multiple stories high, very strong! As you said though, it is when you apply loading on the sides that problems occur. The way these boxes are constructed is strictly for horizontal perpendicular loading on the corners. The sides are just thin corrugated steel. If you buried one in a diagonal position, the load would still not be distributed in the way it was designed for, and not be safe for any amount of time.
Don't worry though, there is a way if you still want to use shipping containers.
Here is a link To an article at container auction.com. They explain the most cost effective way to bury a container is using gabion baskets filled with rocks, or more expensively poured
concrete.
Although as they say in their article, if you want to cover the top with earth you will need a truss system that interfaces either with the gabions or the corners of the container, since the roof cannot handle a distributed load like soil. And at that point you've pretty much built an
underground home so there is not too much of a need for the container anyway.
After my researching this topic I started to think shipping containers only really make sense if you have a lot of them free, already hanging around where you need them. Buying them, moving them, retrofitting them for livability, and other things that go along with them make them a very high
energy undertaking, even though it appears to be recycling on the surface. I could see myself using one as a temporary storage shed or garage, but most likely not more than that.
Good luck!