A friend of mine had a friend some years ago that decided to build a basement under his existing house in southern CA. Tim went down to see what had been accomplished, which was a lot: the hole took up almost the same footprint as the house.

Then Tim started sweating. "Uh, Ernie, where's the support for the house?"

"Support?"

Countrymouse, have you ever seen the 60s movie The Great Escape? Try it, you'll like it. (This from a woman who has only seen 2 good war movies in her life...)

Sue